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Question
Expand the following, using suitable identity:
(–2x + 5y – 3z)2
Solution
It is known that,
(x + y + z)2 = x2 + y2 + z2 + 2xy + 2yz + 2zx
(–2x + 5y – 3z)2 = (–2x)2 + (5y)2 + (–3z)2 + 2(–2x)(5y) + 2(5y)(–3z) + 2(–3z)(–2x)
= 4x2 + 25y2 + 9z2 – 20xy – 30yz + 12xz
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