Binomial Theorem 1 Question 13

14. The coefficient of t4 in the expansion of 1t61t is

(a) 12

(b) 10

(c) 15

(d) 14

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Answer:

Correct Answer: 14. (a)

Solution:

  1. Clearly, 1t61t=(1t6)3(1t)3

Coefficient of t4 in (1t6)3(1t)3

= Coefficient of t4 in (1t183t6+3t12)(1t)3

= Coefficient of t4 in (1t)3

=3+41C4=6C4=15

( coefficient of xr in (1x)n=n+r1Cr)



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