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B
a2r=an−r
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C
ar=a2n−r
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D
none of these
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Solution
The correct option is Car=a2n−r We have ∑2nr=0ar(1x)r=(1+1x+1x2)n=1x2n(x2+x+1)n ⇒∑2nr=0arx2n−r=(x2+x+1)n=∑2nr=0arxr Equating the coefficients of x2n−r on both sides, we get ar=a2n−r for 0≤r≤2n