Questions
If the coefficient of and terms in the expansion of are in A.P ., then the value of is
a
5,9
b
6,9
c
7,9
d
none of these
detailed solution
Correct option is A
The coefficient of f(r+1)th term in the expansion of (1+x)14 is 14CrIt is given that 14Cr−1,14Cr,14Cr+1 are in A.P.⇒ 214Cr=14Cr−1+14Cr+1⇒ 2= 14Cr−1 14Cr+ 14Cr+1 14Cr⇒ 2=r15−r+14−rr+1⇒ 2(15−r)(r+1)=r2+r+210−29r+r2⇒ 4r2−56r+180=0⇒ r2−14r+45=0⇒r=5,9.Talk to our academic expert!
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lf the term independent of x in the expansion of is k, then 18k is equal to
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