If A=∑nr=0(nCrcos(n−r)x.sinrx),B=2nsinnx and C=1!0!n−1+1!3!n−3+1!5!n−5+⋯+1!n−1!1, then
A
A=B2
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B
A=!nCB2n
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C
A=3!n2n−1BC
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D
A=BC
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Solution
The correct options are AA=B2 BA=!nCB2n C=1!n(1!0!n−1+1!3!n−3+1!5!n−5+⋯+1!n−1!1)=1!n(nC1+nC3+⋯+nCn−1)C=2n−2n!B=2nsinnxA=nC1cos(n−1)xsinx+nC2cos(n−2)xsin(2x)+⋯+nCn−1cosxsin(n−1)x+nCnsin(nx).A=nCnsin(nx)+nCn−1cosxsin(n−1)x+nCn−2cos(n−2)xsin(2x)+⋯+nC1cos(n−1)xsinx2A=2nCnsin(nx)+nC1(cos(n−1)xsinx+cosxsin(n−1)x)+nC2(cos(n−2)xsin(2x)+cos(2x)sin(n−2)x)+⋯+nCn−1(cosxsin(n−1)x+cos(n−1)xsinx)=2sin(nx)+(sin(nx))(nC1+nC1+⋯+nCn−1)2A=2sin(nx)+(sin(nx))(2n−2)2A=2nsin(nx)A=2n−1sin(nx)HenceA=B2andA=!n2n2nsin(nx)2n−1!n⇒A=!nCB2n