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Help with this question, answer in textbook is not the same as what I got :(

Hey guys, I've done this question twice now and am still not getting the right answer, HELP PLEASE!!!

(2x+3x)^3(5-x)^3
using the binomial theorem, find the co-efficient of the term of x^3

Reply 1

StephenNeill

What did you get, and what did the textbook say?

A brief description of your working would be nice too.

(edited 12 years ago)

Reply 2

steve2005

Original post by redwalls

Hey guys, I've done this question twice now and am still not getting the right answer, HELP PLEASE!!!

(2x+3x)^3(5-x)^3
using the binomial theorem, find the co-efficient of the term of x^3

I don't think the first bracket is correct.

Reply 3

redwalls

Original post by steve2005

I don't think the first bracket is correct.

oh wow yeah, the first bracket is meant to say (2+3x)^3

Reply 4

redwalls

Original post by StephenNeill

What did you get, and what did the textbook say?

A brief description of your working would be nice too.

so I did, (2+3x)^3 = 3x2x1/3! x (3x)^3
= 27x^3

(5-x)^3 = 3x2x1 / 3! x (-x)^3
= -x^3

so then multiply the two answers and get -27x^6 so the co-efficient of x^3 is -27

but the textbook says -143