Questions
If
then is equal to
detailed solution
Correct option is A
Dividing by (20)19, we can write k=1+2x+3x2+…+20x19 where x = 21/20. k=ddxx+x2+…+x20=ddxxx20−1x−1=(x−1)21x20−1−xx20-1)(x−1)2=20x21−21x20+1(x−1)2But 20x21−21x20 =20212021−21212021=0∴ k=1(21/20−1)2=400Similar Questions
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