Question

If (2x+a)(2x+b)=4x^2-4x+ab, then a+b = ?

A. -4
B. -2
C. -1
D. 2
E. 4

Answer 1

Answer: a+b = -2

B. -2

Because if a = 1 and b = -3 then

(2x+a)(2x+b)=4x^2-4x+ab

Plug in a = 1 and b = -3 into (2x+a)(2x+b) then solve

(2x+a)(2x+b)

= (2x + 1)(2x - 3)

= 4x^2 + 2x - 6x - 3

= 4x^2 - 4x - 3 (so ab = - 3)