I need help factoring 2y^2-2y-24. The answer I got was 2(y+3)(y+3). However the correct answer is 2(y+3)(y-4).

Answer 1

If you had expanded your answer, you would have seen that it was wrong.
How could you possible end up with those negative terms in the original when everything you have is positive ???

2y^2-2y-24
= 2(y^2 - y - 12)
what are two numbers that when multiplied yield -12 and have a sum = -1 ?
Clearly -4 and 3
so...
2(y^2 - y - 12)
= 2(x - 4)(x + 3)