Question

Factor completely 81x^2 - 4.

a. (2x - 9)(2x - 9)
b. (2x - 9)(2x + 9)
c. (9x - 2)(9x - 2)
d. (9x - 2)(9x + 2)

Answer 1

\(\bf 81x^2 - 4\qquad \qquad 81=9^2\qquad \qquad 4=2^2\qquad thus\\ \quad \\
81x^2 - 4\implies 9^2x^2-2^2\implies (9x)^2-2^2\\ \quad \\
\textit{recall that }\quad a^2-b^2 = (a-b)(a+b)
\)

Answer 2

\[81x ^{2}-4\]

Since they are both perfect squares, just take the square root of each.

(9x+2)(9x-2)
so D

Answer 3

thank you!cx

Answer 4

yw