Question

Factor 2x 4 - 20x 2 - 78.

A) 2(x2 - 3)(x2 - 13)
B). 2(x2 + 3)(x2 - 13)
C). 2(x2 - 3)(x2 + 13)

Answer 1

Divide everything by 2: 2(x4-10x2-39). Now factor: 2(x2+3)(x2-13) or B. We know it's not A because the last variable is negative so the signs must be different. :)

Answer 2

2(x^4 - 10x^2 - 39)
2(x^2 - 13)(x^2 + 3)

Letter B