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BilingualMathematicsEduca tionBilingualMathematicsE ducationBilingualMathemat icsEducationBilingualMath ematicsEducationBilingual MathematicsEducationBilin gualMathematicsEducationB ilingualMathematicsEducat ionBilingualMathematicsEd ucationBilingualMathemati csEducationBilingualMathe maticsEducationBilingualM athematicsEducationBiling ualMathematicsEducationBi lingualMathematicsEducati DIFFERENTIAL EQUATION II TASK COMPILATION 3/27/2014 MARIA PRISCILLYA PASARIBU IDN. 4103312018

Task compilation - Differential Equation II

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Page 1: Task compilation - Differential Equation II

BilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationBilingualMathematicsEducationhjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqw

DIFFERENTIAL EQUATION II

TASK COMPILATION

3/27/2014

MARIA PRISCILLYA PASARIBUIDN. 4103312018

Page 2: Task compilation - Differential Equation II

TASK I (February, 13th 2014)

Determine the solution of::

1.d2 yd t2

βˆ’2dydt

βˆ’5 y=0, y(0)=0; y’(0)=1

2.d2 yd t2

βˆ’3dydt

=0, y(0)=0; y’(0)=1

3.d2 yd t2

βˆ’4dydt

βˆ’4 y=0, y(0)=0; y’(0)=1

Solution:

1.d2 yd t2

βˆ’2dydt

βˆ’5 y=0, y(0)=0; y’(0)=1

Characteristic Equation: Ξ»2βˆ’2 Ξ»βˆ’5=0

Ξ»1,2=βˆ’b±√b2βˆ’4 ac

2a=

βˆ’(βˆ’2 )±√ (βˆ’2 )2βˆ’4 (1 ) (βˆ’5 )2 (1 )

¿ 2±√4+202

=2±√242

=2±2√62

=1±√6

Ξ»1and Ξ»2 are real and distinct, then y=c1 em1x+c2 e

m2 x

y (0 )=0

0=c1+c2

c1=βˆ’c2 .................... (1)

y ' (0 )=1

y ' (x )= (1+√6 )c1e(1+√6 )x+(1βˆ’βˆš6 )c1 e

(1βˆ’βˆš6) x

1=(1+√6 ) c1+(1βˆ’βˆš6 )c2

1=(1+√6 ) c1+(1βˆ’βˆš6 )(βˆ’cΒΏΒΏ1)ΒΏ

1=c1 (1+√6βˆ’1+√6 )

1=2√6c1

Page 3: Task compilation - Differential Equation II

c1=1

12√6

c1=βˆ’c2 .................... (1)

c2=βˆ’112

√6

Maka, y=1

12√6e (1+√6 ) xβˆ’ 1

12√6e (1βˆ’βˆš6) x

2.d2 yd t2

βˆ’3dydt

=0, y(0)=0; y’(0)=1

Characteristic Equation:Ξ»2βˆ’3 Ξ»=0

Ξ» (Ξ»βˆ’3)=0

λ1=0∨ λ2=3

Ξ»1and Ξ»2 are real and distinct, then y=c1 em1x+c2 e

m2 x

y=c1 e0x+c2 e

3 x

y (0 )=0

0=c1+c2

c1=βˆ’c2 .................... (1)

y ' (0 )=1

y ' (x )=3c23 x

1=3c2

c2=13

c1=βˆ’13

Then, y=βˆ’13em1 x+ 1

3em2 x

3.d2 yd t2

βˆ’4dydt

βˆ’4 y=0, y(0)=0; y’(0)=1

Page 4: Task compilation - Differential Equation II

Characteristic Equation:Ξ»2βˆ’4 Ξ»βˆ’4=0

Ξ»1,2=βˆ’b±√b2βˆ’4 ac

2a=

βˆ’(βˆ’4 )±√ (βˆ’4 )2βˆ’4 (1 ) (βˆ’4 )2 (1 )

¿ 4±√16+162

=4 ±4√22

=2±2√2

Ξ»1and Ξ»2 are real and distinct, then y=c1 em1x+c2 e

m2 x

y=c1 e(2+2√2) x+c2 e

(2βˆ’2√2 )x

y (0 )=0

0=c1+c2

c1=βˆ’c2 .................... (1)

y ' (0 )=1

y ' (x )= (2+2√2 )c1 e( 2+2√2)x+(2βˆ’2√2)c2e

(2βˆ’2√2)x

1=( 2+2√2 ) c1+(2βˆ’2√2)c2

1=( 2+2√2 ) c1+(2βˆ’2√2)(βˆ’c1)

1=c1(2+2√2βˆ’2+2√2)

1=c1(4√2)

c1=18

√2

c1=βˆ’c2 .................... (1)

c2=βˆ’18

√2

Maka, y=18

√2e(2+2√2) xβˆ’18√2e(2βˆ’2√2) x

Page 5: Task compilation - Differential Equation II

TASK II (February, 20th 2014)

Solve these equation:

1.d4 yd x4 +10

d2 yd x2 +9 y=0

2.d4 yd x4 + d

3 yd x3 + d

2 yd x2 +2 y=0

3. y ' ' '+4 y '=0

4. y ( 4)+4 y ' 'βˆ’ y '+6 y=0

5.d6 yd x6 βˆ’4

d5 yd x5 +16

d4 yd x4 βˆ’12

d3 yd x3 +41

d2 yd x2 βˆ’8

dydx

+26 y=0

Solution:

1.d4 yd x4 +10

d2 yd x2 +9 y=0

Characteristic equation: Ξ»4+10 Ξ»2+9=0

(Ξ»2+9 ) (Ξ»2+1 )=0

( Ξ»+3i ) ( Ξ»βˆ’3 i) ( Ξ»+i ) ( Ξ»βˆ’i )=0

Ξ»1=βˆ’3 i⋁ Ξ»2=βˆ’3 i⋁ Ξ»3=βˆ’i⋁ Ξ»3=i

So, the solution is y=C1 cos3 x+C2 sin3 x+C3cos x+C4 sin x

2.d4 yd x4 + d

3 yd x3 + d

2 yd x2 +2 y=0

Characteristic equation: Ξ»4+Ξ»3+ Ξ»2+2=0

(Ξ»2βˆ’Ξ»+1 ) ( Ξ»2+2 Ξ»+2 )=0

(Ξ»2βˆ’Ξ»+1 )=0

Ξ»1,2=βˆ’b±√b2βˆ’4 ac

2a

Ξ»1,2=βˆ’(βˆ’1)±√(βˆ’1)2βˆ’4(1)(1)

2(1)

Ξ»1,2=1±√1βˆ’4

2

Page 6: Task compilation - Differential Equation II

λ1,2=1±√3i

2

Ξ»1=12+ 1

2√3i and λ2=

12βˆ’1

2√3 i

(Ξ»2+2Ξ»+2 )=0

Ξ»3,4=βˆ’b±√b2βˆ’4ac

2a

Ξ»3,4=βˆ’(2)±√(2)2βˆ’4 (1)(2)

2(1)

Ξ»3,4=βˆ’2±√4βˆ’8

2

Ξ»3,4=βˆ’2Β±2 i

2

Ξ»3=βˆ’1+i and Ξ»4=βˆ’1βˆ’i

So, the solution is y=e12x(C1 cos

12

√3 x+C2sin12√3x )+eβˆ’x (C3 cos x+C4 sin x )

3. y ' ' '+4 y '=0

Characteristic equation: Ξ»3+4 Ξ»=0

Ξ» ( Ξ»2+4 )=0

Ξ» ( Ξ»+2i ) ( Ξ»βˆ’2i )=0

Ξ»1=0⋁ Ξ»2=βˆ’2 i⋁ Ξ»3=2 i

So, the solution is y=C1+C2cos2 x+C3 sin 2x

4. y ( 4)+4 y ' 'βˆ’ y '+6 y=0

Characteristics equation is Ξ»4+4 Ξ»2βˆ’ Ξ»+6=0

(Ξ»2βˆ’Ξ»+2 ) ( Ξ»2+Ξ»+3 )=0

(Ξ»2βˆ’Ξ»+2 )=0

Ξ»1,2=βˆ’b±√b2βˆ’4 ac

2a

Ξ»1,2=βˆ’(βˆ’1)±√(βˆ’1)2βˆ’4(1)(2)

2(1)

Ξ»1,2=1±√1βˆ’8

2

λ1,2=1±√7 i

2

Page 7: Task compilation - Differential Equation II

Ξ»1=12+ 1

2√7 i and λ2=

12βˆ’1

2√7 i

(Ξ»2+ Ξ»+3 )=0

Ξ»3,4=βˆ’b±√b2βˆ’4ac

2a

Ξ»3,4=βˆ’(1 )±√ (1 )2βˆ’4 (1 ) (3 )

2 (1 )

Ξ»3,4=βˆ’1±√1βˆ’12

2

Ξ»3,4=βˆ’1±√11i

2

Ξ»3=βˆ’1

2+ 1

2√11 i and λ4=

βˆ’12

βˆ’12√11 i

So, the equation is:

y=e12x(C1 cos

12

√7 x+C2sin12√7 x)+e

βˆ’12x(C3 cos

12

√11 x+C4 sin12

√11 x )

5.d6 yd x6 βˆ’4

d5 yd x5 +16

d4 yd x4 βˆ’12

d3 yd x3 +41

d2 yd x2 βˆ’8

dydx

+26 y=0

Characteristic equation is Ξ»6βˆ’4 Ξ»5+16 Ξ»4βˆ’12 Ξ»3+41 Ξ»2βˆ’8 Ξ»+26=0

(Ξ»4+3 Ξ»2+2 ) ( Ξ»2βˆ’4 Ξ»+13 )=0

(Ξ»2+1 ) ( Ξ»2+2 ) (Ξ»2βˆ’4 Ξ»+13 )=0

(Ξ»2+1 )=0

Ξ»1,2=βˆ’b±√b2βˆ’4 ac

2a

Ξ»1,2=0±√0βˆ’4 (1)(1)

2 (1)

Ξ»1,2=Β±βˆšβˆ’4

2

Ξ»1,2=Β±2 i

2

Ξ»1=i and Ξ»2=βˆ’i

Page 8: Task compilation - Differential Equation II

(Ξ»2+2 )=0

Ξ»3,4=βˆ’b±√b2βˆ’4ac

2a

Ξ»3,4=0±√0βˆ’4 (1 ) (2 )

2 (1 )

Ξ»3,4=Β±βˆšβˆ’8

2

λ3,4=±2√2 i

2

Ξ»3=√2i and Ξ»4=βˆ’βˆš2 i

(Ξ»2βˆ’4 Ξ»+13 )=0

Ξ»5,6=βˆ’b±√b2βˆ’4ac

2a

Ξ»5,6=βˆ’(βˆ’4)±√(βˆ’4)2βˆ’4 (1 ) (13 )

2 (1 )

Ξ»5,6=4±√16βˆ’52

2

Ξ»5,6=4Β±6 i

2

Ξ»5=2+3 i and Ξ»6=2βˆ’3 i

So, the solution is

y=C1 cos x+C1 sin x+e2 x (C3cos 3x+C4 sin 3 x )+C5 cos√2x+C5sin √2 x

Page 9: Task compilation - Differential Equation II

TASK III (March 7th, 2014)

1.d3qd t 3

βˆ’5d2qd t2

+25dqdt

βˆ’125q=βˆ’60 e7 t

y(0)=0, y’(0)=1, y”(0)=2

2. y(IV )βˆ’6 y ' ' '+16 y ' '+54 y 'βˆ’225 y=100eβˆ’2x

y (0 )= y ' (0 )= y ' ' (0 )= y ' ' ' (0 )=1

Solution:

1.d3qd t 3

βˆ’5d2qd t2

+25dqdt

βˆ’125q=βˆ’60 e7 t

y(0)=0, y’(0)=1, y”(0)=2

Quadratic equation: Ξ»3βˆ’5 Ξ»2+25 Ξ»βˆ’125=βˆ’60e7 t

Y= yl + yr

Ξ»3βˆ’5 Ξ»2+25 Ξ»βˆ’125=0

(Ξ»βˆ’5ΒΏ(Ξ»+5 i)(Ξ»βˆ’5 i)=0

y l=c1 e5 t+c2 cos5 t+c3 sin 5 t

yr=A0 e7 t

yr'=7 A0 e

7t

yr' '=49 A0 e

7 t

yr' ' '=343 A0e

7 t

Page 10: Task compilation - Differential Equation II

y ' ' 'βˆ’5 y ' '+25 yβˆ’125 y=βˆ’60e7 t

343 A0 e7 tβˆ’245 A0e

7 t+175 A0e7 tβˆ’125 A0 e

7 t=βˆ’60e7 t

148 A0 e7 t=βˆ’60 e7 t

A0=βˆ’60148

=βˆ’1537

yr=βˆ’1537

e7 t

Then, we got the equation is equal to

Y= yl + yr

y (t )=c1 e5 t+c2 cos5 t+c3sin 5 tβˆ’15

37e7 t

Now, we are going to find the value of c1, c2, and c3.

y(0)=0

0=c1+c2βˆ’1537

c1+c2=1537

........................................ (1)

y’(0)=1

y ' (t)=5 c1 e5tβˆ’5c2 sin5 t+5c3cos 5tβˆ’105

37e7 t

1=5c1+5c3βˆ’10537

c1+c3=142185

.................................... (2)

y”(0)=2

y ' '( t)=25c1 e5 tβˆ’25c2cos 5tβˆ’25 c3 sin 5 tβˆ’735

37e7 t

2=25c1βˆ’25c2βˆ’73537

25c1βˆ’25c2=80937

c1βˆ’c2=809925

....................................... (3)

Elimination of c2 from (1) and (3)

Page 11: Task compilation - Differential Equation II

c1βˆ’c2=809925

....................................... (3)

c1+c2=1537

........................................ (1)

2c1=809+375

925

c1=592925

From (3), we can get the value of c2 by substituting the value of c1.

c1βˆ’c2=809925

....................................... (3)

592925

βˆ’c2=809925

c2=βˆ’217925

From (2), we can get the value of c3 by substituting the value of c1.

c1+c3=142185

.................................... (2)

592925

+c3=142185

c3=118925

After getting the value of c1, c2, and c3, then the equation is:

y (t )=592925

e5 tβˆ’217925

cos5 t+ 118925

sin 5 tβˆ’1537e7t

2. y ( IV )βˆ’6 y ' ' '+16 y ' '+54 y 'βˆ’225 y=100eβˆ’2x

y (0 )= y ' (0 )= y ' ' (0 )= y ' ' ' (0 )=1

Quadratic equation: Ξ»4βˆ’6 Ξ»3+16 Ξ»2+54 Ξ»βˆ’225=100eβˆ’2x

+

Page 12: Task compilation - Differential Equation II

y= y l+ yr

Ξ»4βˆ’6 Ξ»3+16 Ξ»2+54 Ξ»βˆ’225=0

By using Horner method and ABC formula, so that the roots are gotten:

Ξ»1=3 Ξ»3=3+4 i

Ξ»2=βˆ’3 Ξ»4=3βˆ’4 i

y l=c1 e3 t+c2 e

βˆ’3 t+e3t (c3 cos4 t+c4 sin 4 t)

yr=A0 eβˆ’2x

yr'=βˆ’2 A0 e

βˆ’2t

yr' '=4 A0 e

βˆ’2 t

yr' ' '=βˆ’8 A0 e

βˆ’2t

yr(IV )=16 A0 e

βˆ’2 t

y ( IV )βˆ’6 y ' ' '+16 y ' '+54 y 'βˆ’225 y=100eβˆ’2 t

16 A0 eβˆ’2 t+48 A0 e

βˆ’2t+64 A0 eβˆ’2 tβˆ’108 A0 e

βˆ’2 tβˆ’225 A0 eβˆ’2 t=100eβˆ’2 t

βˆ’205 A0 eβˆ’2 t=100eβˆ’2 t

A0=βˆ’100205

=βˆ’2041

So, the value of yr is

yr=βˆ’20

41eβˆ’2 t

y=c1 e3 t+c2 e

βˆ’3t+e3 t(c3 cos4 t+c4sin 4 t)βˆ’2041eβˆ’2 t

Now, we are going to find the value of c1, c2, and c3.

y(0) = 1

Page 13: Task compilation - Differential Equation II

1=c1+c2+c3βˆ’2041

c1+c2+c3=6141

....................................... (1)

y’(0)=1

y '=3c1 e3 tβˆ’3c2e

βˆ’3 t+3e3 t (c3 cos 4 t+c4 sin 4 t )+e3 t (βˆ’4 c3sin 4 t+4c4 cos 4 t )+ 4041eβˆ’2 t

1=3c1βˆ’3 c2+3c3+4 c4+4041

3c1βˆ’3c2+3c3+4c4=141

........................ (2)

y’’(0)=1

y ' '=9c1 e3 t+9c2 e

βˆ’3 t+9e3 t (c3 cos4 t+c 4sin 4 t )+3e3 t (βˆ’4c3 sin 4 t+4 c4 cos 4 t )+3e3 t (βˆ’4c3 sin 4 t+4 c4 cos4 t )βˆ’16e3 t (c3cos 4 t+c4 sin 4 t )+ 8041eβˆ’2t

1=9c1+9c2+9c3+12c4+12c4βˆ’16 c3βˆ’8041

1=9(c1+c2+c3)+24 c4βˆ’16c3βˆ’8041

12141

=9( 6141

)+24 c4βˆ’16 c3

βˆ’42841

=24 c4βˆ’16 c3

2c3βˆ’3c4=10782

.......................................... (3)

y’’’(0)=1

y ' ' '=27 c1 e3 tβˆ’27 c2 e

βˆ’3 t+75e3 t (c3 cos4 t+c4 sin 4 t )βˆ’100e3t (βˆ’c3sin 4 t+c4 cos4 t )+ 16041eβˆ’2t

1=27 c1βˆ’27c2+75 c3βˆ’100c4+16041

Page 14: Task compilation - Differential Equation II

27c1βˆ’27 c2+75c3βˆ’100c4=βˆ’119

41 ........ (4)

To get the value of c1, c2, c3, and c4, we can use elimination and substituion method from the

above equations.

From (4) and (2), we can get the new equation:

27c1βˆ’27 c2+75c3βˆ’100c4=βˆ’119

41 ........ (4)

27c1βˆ’27 c2+27c3+36c4=9

41 ................ (2)

43 c3βˆ’136c4=βˆ’128

41

6c3βˆ’176 c4=βˆ’1641

..................................... (5)

From (5) and (3), we can get the value of c4.

6c3βˆ’176 c4=βˆ’1641

..................................... (5)

6c3βˆ’9c4=32182

... ....................................... (3)

βˆ’8c4=βˆ’32βˆ’321

82

c4=βˆ’353656

From (3), we can get the value of c3.

2c3βˆ’3(βˆ’353656

)=10782

.......................................... (3)

2c3=1915656

c3=19151315

+

+

Page 15: Task compilation - Differential Equation II

From (1), we get:

c1+c2+19151315

=6141

....................................... (1)

c1+c2=37

1312 ................................................ (6)

From (2), we get:

3c1βˆ’3c2+3( 19151315

)+4 (βˆ’353656

)= 141

........................ (2)

3c1βˆ’3c2=32βˆ’5745βˆ’2824

1312

3c1βˆ’3c2=βˆ’85371312

c1βˆ’c2=βˆ’85373936

................................................ (7)

From (6) and (7), we can get the value of c1 and c2 by elimination method.

c1+c2=37

1312 ................................................ (6)

c1βˆ’c2=βˆ’85373936

............................................. (7)

2c1=βˆ’8537+111

3936

2c1=βˆ’84263936

c1=βˆ’42133936

From (7), we can get the value of c2.

βˆ’42133936

βˆ’c2=βˆ’85373936

............................................. (7)

c2=8537βˆ’4213

3936

+

Page 16: Task compilation - Differential Equation II

c2=1081656

After getting the value of c1, c2, c3, and c4, we get the characteristic value.

y=βˆ’42133936

e3 t+ 1081656

eβˆ’3 t+e3 t( 19151315

cos4 tβˆ’353656

sin 4 t )βˆ’2041eβˆ’2 t

TASK IV (March 13th, 2014)

1.d2qd t 2

+1000dqdt

+25000q=24

q ( 0 )=q ' (0 )=0

2.d2 yd t2

βˆ’4dydt

+ y=2t 3+3 t2βˆ’1

y (0 )= y ' (0 )=1

Solution:

1. q ' '+1000q '+25000q=24

Quadratic equation:

t 2+1000 t+25000=0

Page 17: Task compilation - Differential Equation II

t 1,2=βˆ’b±√b2βˆ’4 ac

2a

t 1,2=βˆ’1000±√(1000)2βˆ’4 (1 ) (25000 )

2 (1 )

t 1,2=βˆ’1000±√900000

2

t 1,2=βˆ’1000Β±300√10

2

t 1,2=βˆ’500Β±150√10

t 1=βˆ’500+150√10 and t 2=βˆ’500βˆ’150√10

q l=c1 e(βˆ’500+150 √10 )t+c2e

(βˆ’500βˆ’150 √10 )t

qr=A0

q ' r=0

q ' ' r=0

q ' '+1000q '+25000q=24

0+1000 (0)+25000(A0)=24

A0=3

3125, then

qr=3

3125

q=q l+qr

q (t)=c1 e(βˆ’500+150 √10) t+c2 e

(βˆ’500βˆ’150√10) t+ 33125

q ( 0 )=0

0=c1+c2+3

3125

c1+c2=βˆ’3

3125 ...................................(1)

q ' (t)= (βˆ’500+150√10 ) c1 e(βˆ’500+150 √10) t+(βˆ’500βˆ’150√10 )c2 e

(βˆ’500βˆ’150√10) t

q ' (0 )=0

Page 18: Task compilation - Differential Equation II

0=(βˆ’500+150√10 )c1+(βˆ’500βˆ’150√10 )c2 ........................... (2)

By using elimination method, we can find the value of c1 from (1) and (2).

(βˆ’500βˆ’150√10 )c1+(βˆ’500βˆ’150√10 )c2=βˆ’3

3125(βˆ’500βˆ’150√10 )

(βˆ’500+150√10 )c1+ (βˆ’500βˆ’150 √10 )c2=0

βˆ’300√10c1=βˆ’3

3125(βˆ’500βˆ’150√10 )

c1=βˆ’5√10βˆ’15

3125

By using (1), we can find the value of c2.

c1+c2=βˆ’3

3125

βˆ’5√10βˆ’153125

+c2=βˆ’3

3125

c2=5√10+12

3125

After finding the value of c1 and c2, we get the equation.

q (t)=(βˆ’5√10βˆ’153125 )e (βˆ’500+150 √10) t+( 5√10+12

3125 )e (βˆ’500βˆ’150√10) t+ 33125

2. y ' 'βˆ’4 y '+ y=2t 3+3 t2βˆ’1

Quadratic equation:

t 2βˆ’4 t+1=0

t 1,2=βˆ’b±√b2βˆ’4 ac

2a

t 1,2=βˆ’(βˆ’4)±√(βˆ’4)2βˆ’4 (1 ) (1 )

2 (1 )

t 1,2=4±√12

2

–

Page 19: Task compilation - Differential Equation II

t 1,2=4±2√3

2

t 1,2=2±√3

t 1=2+√3 and t 2=2βˆ’βˆš3

y l=c1 e(2+√3 ) t+c2 e

( 2βˆ’βˆš3 ) t

yr=A3 t3+A2 t

2+A1t+A0

y 'r=3 A3 t2+2 A2t+A1

y ' 'r=6 A3 t+2 A2

y ' 'βˆ’4 y '+ y=2t 3+3 t2βˆ’1

(6 A3t+2 A2 )βˆ’4 (3 A3 t2+2 A2 t+A1)+(A3 t

3+A2t2+A1t+A0 )=2 t3+3 t 2βˆ’1

A3 t3+(βˆ’12 A3+A2 )t 2+(6 A3βˆ’8 A2+A1 ) t+A1+A0=2 t3+3 t 2βˆ’1

Equation similarity:

A3=2

βˆ’12 A3+A2=3

βˆ’12(2)+A2=3

A2=27

6 A3βˆ’8 A2+A1=0

6 (2)βˆ’8(27)+A1=0

A1=204

A1+A0=βˆ’1

204+A0=βˆ’1

A0=βˆ’205

yr=2t 3+27 t 2+204 tβˆ’205

y= y l+ yr

y (t )=c1 e( 2+√3) t+c2 e

(2βˆ’βˆš3) t+2 t 3+27 t2+204 tβˆ’205

y (0)=1

1=c1+c2βˆ’205

Page 20: Task compilation - Differential Equation II

c1+c2=206 .........................(1)

y '(t )=(2+√3 ) c1e(2+√3) t+(2βˆ’βˆš3 )c2 e

(2βˆ’βˆš3) t+6 t2+54 t+204

y '(0)=1

1=( 2+√3 )c1+(2βˆ’βˆš3 )c2+204

(2+√3 )c1+ (2βˆ’βˆš3 )c2=βˆ’203 ........................... (2)

By using elimination and substitution method, the value of c1 and c2 can be obtained

from (1) and (2).

βˆ’203=(2+√3 )c1+( 2βˆ’βˆš3 )c2........................... (2)

206=(2βˆ’βˆš3 )c1+(2βˆ’βˆš3 )c2 ...................................(1)

2√3 c1=βˆ’203βˆ’206 (2βˆ’βˆš3 )

2√3 c1=βˆ’715+206√3

c1=βˆ’715√3+618

6

c1+c2=206

(βˆ’715√3+6186 )+c2=206

c2=715√3+618

6

y (t )=(βˆ’715√3+6186 )e (2+√3) t+(715√3+618

6 )e( 2βˆ’βˆš3 )t+2 t3+27 t 2+204 tβˆ’205

TASK V (March 20th, 2014)

1.d2 xd t 2

+4dxdt

+8x=(20 t 2+16 tβˆ’78)e2 t

y(0)=y’(0)=0

2.d3qd t 3

βˆ’5d2qd t2

+25dqdt

βˆ’125q=(βˆ’500 t2+465 tβˆ’387)e2 t

q(0)=q’(0)= q’’(0)=0

Solution:

–

Page 21: Task compilation - Differential Equation II

1.d2 xd t 2

+4dxdt

+8x=(20 t 2+16 tβˆ’78)e2 t

y(0)=y’(0)=0

quadratic equation is

Ξ»2+4 Ξ»+8=0

Ξ»1,2=βˆ’b±√b2βˆ’4 ac

2a

Ξ»1,2=βˆ’4±√42βˆ’4 (1)(8)

2(1)

Ξ»1,2=βˆ’4Β±βˆšβˆ’16

2

Ξ»1,2=βˆ’2Β±2 i

y l=eβˆ’2t (c1cos 2t+c2 sin2 t)

yr=(A2t2+A1t+A0)e

2 t

y 'r=(2 A2t+A1 )e2 t+(A2t2+A1t+A0) (2e2 t )

y ' 'r=2 A2 e2 t+(2 A2 t+A1 ) ( 2e2 t )+( 2 A2t+A1 ) (2e2 t )+(A2 t

2+A1t+A0)( 4e2 t )

y ' '+4 y '+8 y=(20 t 2+16 tβˆ’78)e2t

2 A2 e2 t+( 2 A2t+A1 ) (2e2 t )+ (2 A2t+A1 ) (2e2 t )+(A2 t

2+A1t+A0 ) ( 4e2t )+4 {( 2 A2 t+A1 )e2 t+(A2 t2+A1 t+A0) (2e2 t )}+8 {(A2t

2+A1 t+A0)e2 t }=(20 t 2+16 tβˆ’78)e2 t

(2 A2+8 A1+20 A0 )e2 t+(16 A2+20 A1 ) t e2 t+(20 A2)t2e2 t=(20 t 2+16 tβˆ’78)e2t

20 A2=20

A2=1

16 A2+20 A1=16

16(1)+20 A1=16

20 A1=0

A1=0

2 A2+8 A1+20 A0=βˆ’78

2 (1 )+8 (0 )+20 A0=βˆ’78

20 A0=βˆ’78βˆ’2

20 A0=βˆ’80

A0=βˆ’4

Page 22: Task compilation - Differential Equation II

yr=(t 2βˆ’4)e2 t

y = yl + yr

y (t )=eβˆ’2 t (c1cos 2t+c2sin 2 t )+(t 2βˆ’4)e2 t

y ' (t )=(βˆ’2eβˆ’2 t ) (c1 cos2 t+c2sin 2 t )+eβˆ’2t (βˆ’2c1 sin 2t+2c2cos2 t )+2 t e2 t+(t 2βˆ’4) (2e2 t )

y (0 )=0

0=c1βˆ’4

c1=4

y ' (0 )=0

0=βˆ’2c1+2c2βˆ’8

8=βˆ’2(4)+2c2

c2=8

y (t )=eβˆ’2 t (4cos 2t+8 sin 2 t )+(t2βˆ’4)e2t

2.d3qd t 3

βˆ’5d2qd t2

+25dqdt

βˆ’125q=(βˆ’500 t 2+465 tβˆ’387 )e2 t

q(0)=q’(0)= q’’(0)=0

Quadratic equation is:

Ξ»3βˆ’5 Ξ»2+25 Ξ»βˆ’125=0

Ξ»1=5 Ξ»2=5 i

Ξ»3=βˆ’5 i

y l=c1 e5 t+c2 cos5 t+c3 sin 5 t

yr=(A2t2+A1t+A0)e

2 t

y ' r=( 2 A2t+A1 )e2 t+(A2 t2+A1t+A0)(2eΒΏΒΏ2 t)ΒΏ

ΒΏ2 A2t e2t+A1 e

2 t+2 A2 t2 e2 t+2 A1t e

2 t+2 A0e2 t

Page 23: Task compilation - Differential Equation II

y ' 'r=2 A2 e2 t+8 A2t e

2 t+2 A1 e2 t+4 A2t e

2 t+4 A2t2e2 t+2 A1 e

2 t+4 A1 t e2 t+4 A0 e

2t

y ' ' ' r=12 A2e2 t+12 A1 e

2 t+8 A0 e2 t+24 A2t e

2 t+8 A1t e2 t+8 A2t

2 e2 t

y ' ' 'βˆ’5 y ' '+25 y 'βˆ’125 y=(βˆ’500 t 2+465 tβˆ’387 )e2 t

12 A2 e2 t+12 A1 e

2t+8 A0 e2 t+24 A2 t e

2t+8 A1 t e2t+8 A2 t

2 e2 tβˆ’5 {2 A2 e2 t+8 A2t e

2 t+2 A1e2 t+4 A2t e

2 t+4 A2t2e2 t+2 A1 e

2 t+4 A1 t e2 t+4 A0 e

2t }+25 {2 A2 t e2 t+A1 e

2t+2 A2t2 e2 t+2 A1 t e

2 t+2 A0 e2 t }βˆ’125 {(A2 t

2+A1t+A0 )e2 t }=(βˆ’500 t 2+465 tβˆ’387 )e2 t

(2 A2+17 A1βˆ’87 A0 )e2t+ (34 A2βˆ’87 A1 ) t e2 t+(βˆ’87 A2) t 2 e2 t=βˆ’500 t2 e2t+465 t e2 tβˆ’387e2t

βˆ’87 A2=βˆ’500

A2=50087

34 A2βˆ’87 A1=465

34 (50087 )βˆ’87 A1=465

A1=βˆ’23455

7569

2 A2+17 A1βˆ’87 A0=βˆ’387

2( 50087 )+17 (βˆ’23455

7569 )βˆ’87 A0=βˆ’387

A0=2617468658503

yr=( 50087t 2βˆ’23455

7569t+ 2617468

658503 )e2 t

y= y l+ yr

y (t )=c1e5 t+c2 cos5 t+c3sin 5 t+( 500

87t 2βˆ’23455

7569t+ 2617468

658503 )e2 t

y ' (t)=5 c1 e5tβˆ’5c2 sin5 t+5c3cos 5t+( 1000

87tβˆ’23455

7569 )e2 t+(50087t 2βˆ’23455

7569t+ 2617468

658503 ) (2e2 t )

y ' ' (t )=25c1 e5 tβˆ’25c2cos 5tβˆ’25c3 sin 5 t+ 1000

87e2 t+(1000

87tβˆ’23455

7569 )( 2e2 t )+( 100087

tβˆ’234557569 ) (2e2 t )+( 500

87t 2βˆ’23455

7569t+ 2617468

658503 ) (4 e2 t )

y (0 )=0

Page 24: Task compilation - Differential Equation II

0=c1+c2+2617468658503

c1+c2=βˆ’2617468

658503 ................................... (1)

y ' (0 )=0

0=5c1+5c3βˆ’234557569

+5234936658503

5c1+5c3=βˆ’3194351

658503

c1+c3=βˆ’31943513292515

.................................... (2)

y ' ' (0 )=0

0=25c1βˆ’25c2+1000

87βˆ’46910

7569βˆ’ 46910

7569+ 10469872

658503

25c1βˆ’25c2=βˆ’9876532

658503 .................................... (3)

25c1+25c2=βˆ’65436700

658503 ................................... (1)

50c1=βˆ’75313232

658503

c1=βˆ’7531323232925150

From equation (1), we get the value of c2.

c2=βˆ’2617468

658503+75313232

32925150

c2=βˆ’5556016832925150

From equation (2), we get the value of c3.

c3=βˆ’31943513292515

+ 7531323232925150

c3=4336972232925150

+

Page 25: Task compilation - Differential Equation II

y (t )=βˆ’7531323232925150

e5 tβˆ’5556016832925150

cos5 t+ 4336972232925150

sin 5 t+( 50087t 2βˆ’23455

7569t+ 2617468

658503 )e2 t