Question

Solve 2x2 + x = 15.

x=-5 and x=5
x=3/2 and -5
x=15 and -2
x=5/2 and -3

Please help, thanks

Answer 1

x=5/2 and -3

Explanation:

2x^2 + x = 15.

Subtract 15 from each side

2x^2 + x - 15 =0

Factor

(2x+a ) (x+b ) =0

We need the number to multiply to -15

-1 * 15 -3 *5 -5* 3 -15*1

1* -15 3 * -5 5 * -3 15 * -1

FOIL

2b+a = 1

Take the second number *2 and add the first number . It needs to equal 1

2*15 -1 no

2*5 -3 no

2*3 -5 = 1 yes

(-5 ,3 is the pair)

(2x -5) (x+3) = 0

Using the zero product property

2x-5 = 0 x+3 =0

2x=5 x=-3

x = 5/2 x=-3