Question

factoring expressions

Answer 1

http://prntscr.com/ktrxma

Answer 2

@HanAkoSolo

Answer 3

@SmokeyBrown

Answer 4

Well, the answer I got for this one is
(3x+4)(x^2 - 5)
But I'd be hard-pressed to explain my reasoning.
I guess I started by noting the common factors in the equation. Like, 3x^3 and -15x have a common factor of 3x; 4x^2 and 20 have a common factor of 4. So, I reasoned these must be parts of the factorization.
So that got me the first part, (3x+4)
And then figuring out the second part, (x^2 - 5) was just a matter of finding what I'd need to multiply by (3x +4) to get the final result.
I don't promise this method always works, and there may be a better way to do it, but that's how I got the answer this time.