1.

`int(x^3-x)/(1+x^6)dx` is equal toA. `(1)/(6)log.(x^(4)-x^(2)+1)/(x(x^(2)+1))+C`B. `(1)/(6)tan^(-1).((x^(2)+1)^(2))/(2)+C`C. `log.(x^(4)-x^(2)+1)/((1+x^(2))^(2))+C`D. `tan^(-1).((x^(2)+1)^(2))/(2)+C`

Answer» Correct Answer - A
`I=(1)/(2)int(t-1)/(1+t^(3))dt (" where "t=x^(2))`
`=(1)/(2)int((-2)/(3(1+t))+(1)/(3)((2t-1))/(t^(2)-t+1))dt " (After partial fractions)"`
`=(1)/(6).ln(x^(4)-x^(2)+1)/((x^(2)+1)^(2))+C`


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