Question

5x^2 + 15x

Answer 1

5x(x+3)

Answer 2

5x^2=15x

Move the 15x over to the other side. Now you have:

5x^2 - 15x = 0

Does this look more familiar? More like a quadratic? Now try factoring out the monomial, which is in this case 5x.

5x (x - 3) = 0

What will make 5x = 0? 0.
What will make x-3 = 0? 3.

So your solution set is...
{0, 3}

And, yes, they do each work when you plug them back in!

Answer 3

if you like my answer give it a metal!