How do you factor #4x^2 - 81#?

1 Answer
Don't Memorise
Nov 14, 2015

#color(blue)((2x+9)(2x-9)#

Explanation:

#4x^2−81# can also be expressed as
#(2x)^2-9^2#

Now as per the property :
#color(blue)(a^2-b^2=(a+b)(a-b)# we can re write the expression.

#color(blue)((2x)^2-9^2= (2x+9)(2x-9)#
(here #a=2x, b=9)#

So the factorised form for the expression is
#color(blue)((2x+9)(2x-9)#

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