Concept:Use the substitution x2=t to reduce the integral to a standard form.Explanation:Let I=∫1+x4xdx.Put x2=t, so 2xdx=dt.Hence xdx=2dt.Substituting into the integral:I=21∫1+t2dt.We know ∫1+t2dt=tan−1(t)+c.Therefore, I=21tan−1(t)+c.Now replace t=x2:I=21tan−1(x2)+c.Answer:21tan−1(x2)+c, which matches option A.