Questions
lf the term independent of x in the expansion of is k, then 18k is equal to
a
5
b
7
c
9
d
11
detailed solution
Correct option is B
given binomial is 32x2−13x9So the general term,Tr+1=9Cr32x29−r−13xr=9Cr329−r−13rx18−3rlf the term is independent of x, then 18−3r=0⇒r=6∴(r+1) th term =7th term is independent of xNow, as T6+1=k⇒ 9C6323−136=k⇒ 9×8×73×2×127×8=k⇒k=718⇒18k=7Hence, option (b) is correct.Talk to our academic expert!
Similar Questions
lf some three consecutive coefficients in the binomial expansion of (x + 1)n in powers of x are in the ratio 2 : 15 : 70, then the average of these three coefficients is
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