Question

factorise the following by using suitable identities
a^4-81

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Answer 1

Factorisation :

Using identity

$a^{2} - b^{2} = ( a + b ) ( a - b )$

a = a^2

b =  9^2

$(a^{2})^{2} - 81^{2} = ( a^{2} + 9 ) ( a^{2} - 9 )$