Q.
For the expansion xsinp+x−1cosp10,(p∈R)
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a
the greatest value of the term independent of x is 10!/25(5!)2
b
the least value of sum of coefficient is zero
c
the greatest value of sum of coefficient is 32
d
the least value of the term independent of x occurs when p=(2n+1)π4,n∈Z
answer is A.
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Detailed Solution
xsinp+x−1cosp10The general term in the expansion isTr+1=10Cr(xsinp)10−rx−1cosprFor the term independent of x, we have 10 - 2r = 0 or r = 5.Hence, the independent term is 10C5sin5pcos5p=10C5sin52p32which is the greatest when sin2p = 1.The least value of 10C5sin52p32 is −10!25(5!)2 whensin2p=−1 or p=(4n−1)π4,n∈Z.Sum of coefficient is (sin p + cos p)10, when x = 1or (1 + sin 2p)5, which is least when sin2p = -1.Hence, least sum of coefficients is zero. Greatest sum of coefficient occurs when sin 2p = 1. Hence, greatest sum is 25 = 32.
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