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

Answer:

x=5/2 and -3

Step-by-step 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