Engineering
Mathematics
Binomial Theorem for Negative and Fractional Index
Question

The coefficient of t4 in the expansion of (1−t61−t)3is

15

14

10

12

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Solution

(1–t6)3 (1-t)–3

(1–t18 – 3t6 + 3t12) (1–t)–3

⇒ coefficient of t4 in (1–t)–3 is 3+4-1C4 = 6C2 = 15