Binomial – two terms

Expand(a + b)2

(a + b)3

(a + b)4

Study each answer. Is there a pattern that we can use to simplify our expressions?

Notice that each entry in the triangle corresponds to a value nCr

0C0

1C0 1C1

2C0 2C1 2C2

3Co 3C1 3C2 3C3

so we can see that tn,r = nCr = n!/(r!(n-r)!)

by Pascal’s formula we can see thatnCr = n-1Cr-1 + n-1Cr

 

Rewrite the following using Pascal’s Formula10C4 18C8 + 18C9

The coefficients of each term in the expansion of (a + b)n correspond to the terms in row n of Pascal’s Triangle. Therefore you can write these coefficients in combinatorial form.

Lets look at (2a + 3b)3

= 8a3 + 36a2b +54ab2 + 27b3

Notice that there is one more term than the exponent number!

From Dan

(a + b)n = nC0an + nC1an-1b + nC2an-2b2 + … + nCran-rbr + … + nCnbn

or

n

r

rrnrn

n baCba0

)(

Expand (a + b)5

Try it with (3x – 2y)4

Factoring using the binomial theoremRewrite 1 + 10x2 + 40x4 + 80x6 + 80 x8 + 32x10 in the form (a + b)n

We know that there are 6 terms so the exponent must be five

Step 1

The final term is 32x10

Step 2

Therefore, b =

The first term is 1

Therefore, a =

Step 3

HomeworkPg 293 # 1ace, 3ab, 4bc, 5ac, 8, 9ace,11ad,12a, 16a, 21