Let
I=∫0π/21+cos2xsinxdx Let
cosx=t and
−sinxdx=dt Now,
x=0⇒t=cos0=1 and
x=2π⇒t=cos2π=0∴\mathrm{I}
=∫101+\mathrmt2sinx\left(\frac{-\mathrm{dt}}{\sin \mathrm{x}}\right)=-\int_{1}^{0} \frac{\mathrm{dt}}{1+\mathrmt^{2}}=
[tan−1t]10=−[0−4π]=4π