How do you factor 4x squared minus 81?

Answer 1

(2x - 9)(2x +9)

Answer 2

4x^(2) - 81

First remember the two numbers are both squared numbers.

4 = 2^(2) & 81 = 9^(2)

Hence

(2x)^(2) - 9^(2)

Next remember two squared terms with a negative(-) between them , will factor.

Hence

(2x - 9)(2x + 9)

Note the two different signs.

NB Two squared terms with a positive (+) between them does NOT factor. .

Answer 3

(4x2 - 81) = (2x + 9) (2x - 9)