Questions
In the expansion of , if the sum of the coefficients of is 0, then n is
a
25
b
20
c
15
d
None of these
detailed solution
Correct option is C
x3−1r2nGeneral term Tr+1=n!r!(n−r)!(−1)n−rx5n−2nIf 5r−2n=5, then 5r=2n+5 or r=2n5+1If 5r−2n=10, then 5r=2n+10 or r=2n5+2x5 and x10 terms occurs if n=5kGiven that sum of x5 and x10 is zero.⇒5k!(2k+1)!(3k−1)!−5k!(2k+2)!(3k−2)!=0or 13k−1−12k+2=0or k=3⇒n=15Talk 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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