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If `f(x) = int(5x^(8)+7x^(6))/((x^(2)+1+2x^(7))^(2))dx, (x ge 0)`, and f(0) = 0, then the value of f(1) isA. `-(1)/(2)`B. `-(1)/(4)`C. `(1)/(4)`D. `(1)/(2)` |
Answer» Correct Answer - C We have, `f(x) = int(5x^(8)+7x^(6))/((x^(2)+1+2x^(7))^(2))dx` `=int(5((x^(8))/(x^(14)))+7((x^(6))/(x^(14))))/((x^(2)/(x^(7))+(1)/(x^(7))+(2x^(7))/(x^(7)))^(2))dx` (dividing both numerator and denominator by `X^(14)`) `=int(5x^(-6)+7x^(-8))/((x^(-5)+x^(-7)+2)^(2))dx` Let `x^(-5) + x^(-7)+2 = t` `rArr (-5x^(-6)-7x^(-8))dx = dt` `rArr (5x^(-6)+7x^(-8))dx = - dt` `therefore f(x) = int - (dt)/(t^(2))= - intt^(-2)dt` `= -(t^(-2+1))/(-2+1)+C=-(t^(-1))/(-1)+C=(1)/(t)+C` `=(1)/(x^(-5)+x^(-7)+2)+C=(x^(7))/(2x^(7)+x^(2)+1)+C` `therefore f(0)=0` `therefore 0 = (0)/(0+0+1)+C rArr C = 0` `therefore f(x)=(x^(7))/(2x^(7)+x^(2)+1)` `rArr" "f(1)=(1)/(2(1)^(7)+1^(2)+1)=(1)/(4)` |
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