Question

Which of the following equations is CORRECT?

A. (a + b) (a – b) = a 2 + b 2
C. (a + b) (a – b) = a 2 + ab + ab + b 2
B. (a + b) (a – b) = a 2 − b 2
D. (a + b) (a – b) = a 2 − ab − ab − b 2

Answer 1

Option C, the second one. (B and C are switched)

Explanation:

a * a = a2

a * b = +ab

⬇️

2ab

⬆️

b * a = +ba or +ab

Two b's make b2 and don't worry, even with the negative sign it is a b2.