Question

Which equation involves a prime quadratic and cannot be solved by factoring? A. x2 + 6x + 9 = 0 B. x2 − x − 6 = 0 C. x2 + 3x − 4 = 0 D. x2 + 5x − 4 = 0

Answer 1

$A.\ x^2+6x+9=x^2+3x+3x+9=x(x+3)+3(x+3)=(x+3)(x+3)\\\\B.\ x^2-x-6=x^2+2x-3x-6=x(x+2)-3(x+2)=(x+2)(x-3)\\\\C.\ x^2+3x-4=x^2+4x-x-4=x(x+4)-1(x+4)=(x+4)(x-1)\\\\D.\ x^2+5x-4\leftarrow ANSWER$

Answer 2

The answer is D, because the others can be solved. A when factored is equal to -3, when B is factored it is equal to 3,-1, when C is factored it is 1,-4. D can be solved but you will only get irrational numbers which can't be used.