Binomial question (1 Viewer)

[enigma_1]

How to find the coefficient of x^4 in (3+x)(1-x)^15

Thanks

 

[braintic]

This partially expands to
3(1-x)^15 + 1x(1-x)^15

So the coefficient of x^4 is:

3 times the coefficient of x^4 in (1-x)^15
PLUS
1 times the coefficient of x^3 in (1-x)15

 

[enigma_1]

This partially expands to
3(1-x)^15 + 1x(1-x)^15

So the coefficient of x^4 is:

3 times the coefficient of x^4 in (1-x)^15
PLUS
1 times the coefficient of x^3 in (1-x)15

Sorry was that a "times" sign? Thanks

 

[awesome-0_4000]

No that is an x, he expanded the (3+x) bracket out, multiplying (1-x)^15 by each term of (3+x)

 

[enigma_1]

No that is an x, he expanded the (3+x) bracket out, multiplying (1-x)^15 by each term of (3+x)

thanks