77.3k views
5 votes
Which method is best to factor f(x) = x^2 - 81?

2 Answers

3 votes
use difference of 2 perfect squares

remember that
a^2-b^2=(a-b)(a+b)

so

x^2-81=

x^2-9^2=

(x-9)(x+9)
there, factored
User Bornander
by
8.4k points
3 votes

Use the difference of perfect squares

f(x) = x^2 - 81

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

f(f) = f^2 , f(-9) = -9f , f(9) = 9f , -9(9) = -81

(f(-9)), (f(9)) is your factors

hope this helps

User DK ALT
by
7.9k points

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