# Question 1 : Factorize ( x 2 − 4 x − 5) ( x 2 − 4 x − 12) − 144

Question 1 : Factorize ( x 2 − 4 x − 5) ( x 2 − 4 x − 12) − 144

cross multiplication factorisation, difference of two squares factorisation, greatest common divisor factorisation, how to factorise 4 terms, factorisation method formula

Solution :

We write the given expression;

We see that ​​ is present in first two multiplying terms, so for sake of simplicity we suppose it to be equale to y i-e

suppose ​

==> ​

==>​

==>​

Dividing mid term into two parts such that their sum is (-17y) and their product is ​​. We can think of (-21y) and  (4y) -- so;

==> ​

==>​

or

==> ​

Taking (y-21) as common;

==>  ​

Since we supposed ​

==> ​

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Insert math as
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