Question

What is the solution set of 2x^2 + x = 15?

a) {3, -5/2}
b) {-3, 5/2}
c) {2, -3/2}

Answer 1

b) 2(-3)^2-3=15
( 9x2)-3=15
18-3=15
15=15

Answer 2

2x^2+x-15=0
(2x-5)(x+3)=0.
x=-3, x=5/2

Answer 3

2x^2+x-15=0
2x^2+6x-5x-15=0
2x(x+3)-5(x+3)
(2x-5)(x+3)=0
x=-3,5/2