Question

Choose the correct product of (9x − 5)(9x + 5).

81x2 + 90x + 25
81x2 − 25
81x2 + 25
81x2 − 90x + 25

Answer 1

The Answer is B

Explanation:

(9x−5)(9x+5)

=(9x+−5)(9x+5)

=(9x)(9x)+(9x)(5)+(−5)(9x)+(−5)(5)

=81x2+45x−45x−25

=81x2−25

Answer 2

Hi,
(a+b)(a-b=a²-b²
Thus (9x)²-5²=81x²-25