Concept:Recognise the integrand as
vu multiplied by the derivative of
vu, so its integral is
21(vu)2+c.
Explanation:Recall the quotient rule for differentiating
u and
v with respect to
x:
dxd(vu)=v2vdxdu−udxdvRewrite the given integrand by factoring out
vu:
v31(uvdxdu−u2dxdv)=vu[v2vdxdu−udxdv]Using the quotient rule, the bracketed term is exactly
dxd(vu).
Hence, the integrand becomes:
vu⋅dxd(vu)Let
t=vu.
Then the integral simplifies to:
∫tdxdtdx=∫tdtEvaluating this integral gives:
∫tdt=2t2+cSubstitute
t=vu back to obtain the final result:
21(vu)2+c=2v2u2+cAnswer:2v2u2+cThus, option D is the correct answer.