(2x - 9)(2x +9)
(4x2 - 81) = (2x + 9) (2x - 9)
(2x - 9)(2x - 9) or (2x - 9)2
There is a formula for factoring the "difference of squares." In this case, the answer is (9 - 4x)(9 + 4x)
(9 - 5u)(9 + 5u)
x2-81 = (x-9)(x+9)
I believe it is prime as you have written it. change the end to + 81 and it factors as (2x - 1)(x-9)(x+9)
9x2 - 6xy + y2 - 81 = (3x - y)2 - 81 = (3x - y - 9)*(3x - y + 9)
85
If that's 16x2 + 72x + 81, that factors to (4x + 9)(4x + 9) or (4x + 9)2
Type your answer here... 81
81 x 2 - 16 = 146
9x2 - 6xy + y2 - 81 = (3x - y)2 - 92 = (3x - y - 9)(3x - y + 9)
78 minus78