I am to evaluate the following:

C(7,2)

answer:21

C(12,7)

answer: 66

This is the one I can't figure out

the coefficient of x7y2 in the expansion of (2x-y)9

any help is appreciated

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- Dec 9th 2006, 08:38 AMpapa_chango123check my work
I am to evaluate the following:

C(7,2)

answer:21

C(12,7)

answer: 66

This is the one I can't figure out

the coefficient of x7y2 in the expansion of (2x-y)9

any help is appreciated

- Dec 9th 2006, 09:20 AMSoroban
Hello, papa_chango123!

Quote:

Evaluate: .

. . Answer: 21 . . . Right!

. . Answer: 66 . . . no

Quote:

Find the coefficient of in the expansion of

You're expected to know the Binomial Expansion.

The term with is: .

Hence, we have: .