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Question
Find the coefficient of x in the expansion of (1 – 3x + 7x2)(1 – x)16.
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Solution
The given expression is (1 – 3x + 7x2)(1 – x)16.
= (1 – 3x + 7x2) [16C0(1)16(–x)0 + 16C1(1)15 (–x) + 16C2(1)14 (–x)2 + …]
= (1 – 3x + 7x2) (1 – 16x + 120x2 …)
Collecting the term containing x
We get –16x – 3x = – 19x
Hence, the coefficient of x = –19
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