InterviewSolution
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The value of `(.^(21)C_(1) - .^(10)C_(1)) + (.^(21)C_(2) - .^(10)C_(2)) + (.^(21)C_(3) - .^(10)C_(3)) + (.^(21)C_(4) - .^(10)C_(4)) + … + (.^(21)C_(10) - .^(10)C_(10))` isA. `2^(21) - 2^(11)`B. `2^(21) - 2^(10)`C. `2^(20) - 2^(9)`D. `2^(20) - 2^(10)` |
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Answer» Correct Answer - d We have `+( ""^(21)C_(1)-""^(10)C_(1))+( ""^(21)C_(2)-""^(10)C_(2))( ""^(21)C_(3)-""^(10)C_(3))` `+( ""^(21)C_(4)-""^(10)C_(4))+...+( ""^(21)C_(10)-""^(10)C_(10))` `= ( ""^(21)C_(1)+ ""^(21)C_(2)+ ""^(21)C_(3)+ ""^(21)C_(4) + ...+ ""^(21)C_(10))` `= ( ""^(10)C_(1)+ ""^(10)C_(2)+ ""^(10)C_(3)+ ""^(10)C_(4) + ...+ ""^(10)C_(10))` `=(1)/(2){ ""^(21)C_(1)+2""^(21)C_(2)+ 2""^(21)C_(3)+2""^(21)C_(4)+...+2 ""^(21)C_(10)}` ` -{ ""^(10)C_(1)+ ""^(10)C_(2)+ ""^(10)C_(3)+ ""^(10)C_(4) + ...+ ""^(10)C_(10)}` ` = (1)/(2) {( ""^(21)C_(1)+""^(21)C_(20))+ (""^(21)C_(2)+""^(21)C_(19))+(""^(21)C_(3)+""^(21)C_(18)) ` `+...+(""^(21)C_(10)+""^(21)C_(11))}={""^(10)C_(1)+""^(21)C_(2)` `+""^(10)C_(3)+""^(10)C_(4)+...+ "^(10)C_(10)}` `=(1)/(2) {""^(21)C_(1)+""^(21)C_(2)+""^(21)C_(3)+...+ ""^(21)C_(19) +""^(21)C_(20)}` `-{ ""^(10)C_(1)+ ""^(10)C_(2) + ...+ ""^(10)C_(10)}` `=(1)/(2) {(2^(21)- (""^(21)C_(0)+""^(21)C_(21))}+{2^(10) - ""^(10)C_(0)}` `=(1)/(2) {(2^(21)-2)(2^(10) -1) = 2^(20) - 2^(10)`. |
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