Expand following, using suitable identities :- (3a – 7b – c)^{2}

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#### Solution

It is known that,

(x + y + z)^{2} = x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx

(3a – 7b – c)^{2} = (3a)^{2} + (-7b)^{2} + (-c)^{2} + 2(3a)(-7b) + 2(-7b)(-c) + 2(-c)(3a)

= 9a^{2} + 49b^{2} + c^{2} - 42ab + 14bc - 6ac

Concept: Algebraic Identities

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