Q3 of 86 Page 56

Factorise the following using appropriate identities.

18a2 – 50

Take out common factor 2


⇒ 18a2 – 50 = 2 (9a2 - 25)


Now


9a2 can be written as (3a)2


25 can be written as 52


⇒ 18a2 – 50 = 2 ((3a)2 – 52)


using the identity (a + b) × (a – b) = a2 – b2


here a = 3a and b = 5


therefore 18a2 – 50 = 2 (3a + 5) (3a – 5)


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