Question

Expand the brackets and collect the terms...
(X-4)(X-1)(2x+3)

I worked it out to be 2x^3 - 7x^2 - 23x -12
But when I checked the answers it came to...
2x^3 - 7x^2 - 7x +12

Could anyone explain where I went wrong please?
I think it's just an error with + and - somewhere.

Answer 1

its pretty easy the first 2 brackets open up as the quadratic eq. x^2-5x+4 so multiplying term by term (x^2-5x+4)(2x+3) you get 2x^3 - 7x^2 - 7x +12

Answer 2

Thanks, but where does the -7x come from?

Answer 3

u get a -15x and +8x solving u get -7x

Answer 4

So everything in the first bracket needs to be timed by everything in the second bracket? Because surely there should be an extra 3x^2 in there?

Answer 5

All sorted, thanks.