Use the direct method to evaluate : (3b−1) (3b+1) - Vidyadip

Question

Use the direct method to evaluate : $(3b−1) (3b+1)$

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Answer

Note : $(a+b) (a−b)$
$= a^2 − b^2(3b−1) (3b+1)$
$= (3b)^2− (1)^2$
$= 9b^2 − 1$

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