How do you factor x^2-81?

1 Answer
Alan P.
May 18, 2016

x^2-81=color(green)((x-9)(x+9))

Explanation:

For the general case:
color(white)("XXX")(x^2-a^2)=(x-a)(x+a)

(x^2-81 ) = (x^2-9^2)

substituting 9 for a in the general case gives:
color(white)("XXX")(x-9)(x+9)

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