Factorise: 20 a^2-45 b^2 - Vidyadip

Question

Factorise:
$20 a^2-45 b^2$

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Answer

Using: $a ^2- b ^2=( a + b )( a - b )$
$20 a^2-45 b^2$
$=5\left(4 a^2-9 b^2\right)$
$=5(2 a)^2-(3 b)^2$
$=5(2 a+3 b)(2 a-3 b)$

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