HSG Toan 8 (3).doc

MN: TON 8

Thi gian: 120 pht (Khng k thi gian giao )Bi 1( 2,0 im): Phn tch a thc sau thnh nhn t

a) ( x2 + y2)2 - 4x2y2b) (x-2)(x-1)(x+1)(x+2) - 10

c) x2- 4x -5

Bi 2( 1,5 im): Thc hin php tnh

a)

b)

Bi 3(1,5 im):

a) Chng minh:

b) p cu a thu gn phn thc:

Bi 4( 3,5 im): Hnh thang ABCD (AB // CD) c hai ng cho ct nhau ti O. ng thng qua O v song song vi y AB ct cc cnh bn AD, BC theo th t M v N.

a, Chng minh rng OM = ON.

b, Chng minh rng .

c, Bit SAOB= 20082 (n v din tch); SCOD= 20092 (n v din tch). Tnh SABCD.Bi 5(1,5 im): Cho 2x2+2y2 = 5xy v 0< x < y. Tnh gi tr ca

--------------------- Ht -----------------------

UBND HUYN KIM SNPHNG GIO DC V O TO

HNG DN CHM THI CHN HSG

MN: TON 8

Cup nim

1a) a/=

0,5

b/

0,75

c/ = x2- 5x +x -5 = x(x - 5) +( x - 5) = (x - 5)(x + 1)

0,75

2a/

0,75

b/

0,75

3a/

EMBED Equation.DSMT4 0,75

b/

0,75

40,5

a/ Lp lun c ,

0,5

Lp lun c

0,25

OM = ON

0,25

b/ Xt c (1), xt c (2)

T (1) v (2) OM.()

0,5

Chng minh tng t ON. 0,25

t c (OM + ON).

EMBED Equation.3

0,25

c/ ,

EMBED Equation.3

EMBED Equation.3

0,25

Chng minh c 0,25

Thay s c 20082.20092 = (SAOD)2 SAOD = 2008.20090,25

Do SABCD= 20082 + 2.2008.2009 + 20092 = (2008 + 2009)2 = 40172 (n v DT)0,25

5

1,5

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