If 1+x)n=C0+C1x+C2x2+.......+Cnxnthen the value of C0−C2+C4−C6+.......is
A
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B
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C
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D
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Solution
The correct option is D Since(1+x)n=C0+C1x+C2x2+......+CnxnPutx=i,onboththesides,weget(1+i)n=(C0−C2+C4−.....)+i(C1−C3+C5−.....)........(i)Also,1+i=√2(cosπ4+isinπ4)inamplitudemodulusform⇒(1+i)n=2n/2(cosπ4+isinπ4)n....(ii)Equatingtherealpartsin(i)and(ii)weget,C0−C2+C4−C6+.....=2π/2cosnπ4