It's easier to solve this equation without expanding it.1. (x+5)(x-4)=0
x^2 -4x+5x-20=0
x^2+x-20=0
x^2+x=20
x^2=20-x
x=4
As fan96 has pointed out, I'm amazed you are doing the questions that way. Luckily for you, you now have feedback on your own effort. Try to improve your approach.1. (x+5)(x-4)=0
x^2 -4x+5x-20=0
x^2+x-20=0
x^2+x=20
x^2=20-x
x=4
2. x^2-8x+15=0
x^2+15=8x
x^2=8x-15
x=3