lf (1+x+x2)n=a0+a1x+a2x2+......+a2nx2n then a20−a21+a22−…+a22n=
A
0
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B
an
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C
−an
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D
an−1
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Solution
The correct option is Ban Let us consider n=2 Therefore (1+x+x2)2 =1+x2+x4+2x+2x3+2x2 =1+2x+3x2+2x3+x4 Hence a0=1 a1=2 a2=3 a3=2 a4=1 Therefore a20−a21+a22−a23+a24 =1−4+9−4+1 =11−8 =3 =a2 which implies an This is only satisfied by OptionB