binomial expansion? algebra help ASAP!!?

Question

what is the expansion of (4x-3y)^7 ? i know generally how to do it but how do i find the 5th term?

i am getting 186624x^3 y^4
is this correct???

Answer 1

Not correct. The correct answer is 181440x^3y^4.
You have made a mistake in your calculations
somewhere.

Answer 2

First multiply (4x-3y) times itself 7 times like this
square it you should get 16x^2+ 9y^2 this is 2 of 7
square previous answer you get 256x^4+ 288x^2y^2+ 81y^2
now you have done (4x-3y) times itself four times, multiply second answer by first answer you get
4096x^6+ 6912x^4y^2+ 3888x^2y^4+ 729y^6
that is now (4x-3y) times itself six times
now multiply your third answer by the original (4x-3y)
you should get
16384x^7+ 27648x^5y^2+ 15552x^3y^4+ 2916xy^6
- 122288x^6y- 20736x^4y^3- 11664x^2y^5+ 2187y^7 that is the final answer
*just so you know, ex. 23x^4y means 23 times x (which is raised to the sixth power) times y

I hope you appriciate this it took me a long time to write out on the computer. About 45 minutes, i started typing when you were about 2 minutes in, it took a while to transfer from paper to computer.

Answer 3

neither answer is correct...lol. use pascal's triangle or the binomial theorem, and the final answer should have 8 terms. formatting the answer without equation editor would make it look hopelessly messy, so i won't try. but look it up in your textbook to find some help.

Answer 4

That is correct!