Which expression is prime?

a. x2 + 3x + 2

b. x2 + 8x + 7

c. x2 + 8x - 22

d. x2 + 12x + 27?

Prime means it cannot be factored any more.

the answer is C

A = (x+1) (x+2)

B = (x+1) (x+7)

D = (x+3) (x+9)

But C cannot be factored. If it were x²+9x-22, it would be (x+11) (x-2). but with 8x, it doesn't work.