Question

Solve x^2 - 10x = -21.

A.x= 7 and x = 3
B.x= -7 and x = 3
C.x=-7 and x = -3
D.x= 7 and x = -3

Answer 1

A

Explanation:

1.move -21 over to the other side to get x^2 - 10x +21

2. factor. you want to find something that multiples to 21 (the c value) but adds up to -10 (the b value.) the numbers are -7 and -3. so you would factor it out like this: (x-7)(x-3)

3. set each factor to 0 to find the x values

x-7=0 and x-3=0. once you move the numbers over to isolate the x term, you should get x=7 and x=3.