Coefficient of the term independent of x in the expansion of x+1x2/3−x1/3+1−x−1x−x1/210is
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a
210
b
105
c
70
d
35
answer is A.
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Detailed Solution
We havex+1=x1/33+1=x1/3+1x2/3−x1/3+1,x−1=(x−1)(x+1)and x−x1/2=x(x−1),Thus, x+1x2/3−x1/3+1−x−1x−x1/2 =x1/3+1−1+x−1/2=x1/3−x−1/2Now, the (r+1)th term in the expansion of x1/3−x−1/210 is Tr+1=10Crx1/310−rx−1/2r(−1)r=10Crx103−5r/6(−1)rFor this term to be independent of x, 103−5r6=0 ⇒ r=103×65=4 Thus, coefficient of the term independent of x in the given expression is 10C4=10!4!6!=210.