Chapter 10.1, Problem 77ES

If $f^{\prime }\left(t\right)\text{ and }{g}^{\prime }\left(t\right)$ are continuous functions, and if no segment of the curve $x=f\left(t\right),y=g\left(t\right)\left(a\le t\le b\right)$ is traced more than once, then it can be shown that the area of the surface generated by revolving this curve about the x-axis is $S={\displaystyle {\int }_a^{b}2\pi y\sqrt{{\left(\frac{dx}{dt}\right)}^2+{\left(\frac{dy}{dt}\right)}^2}dt}$ and the area of the surface generated by revolving the curve about the y-axis is $S={\displaystyle {\int }_a^{b}2\pi x\sqrt{{\left(\frac{dx}{dt}\right)}^2+{\left(\frac{dy}{dt}\right)}^2}dt}$ [The derivations are similar to those used to obtain Formulas (4) and (5) in Section 6.5.] Use the formulas above in these exercises.

Find the area of the surface generated by revolving the curve $x={\cos }^{2}t,y={\sin }^{2}t\left(0\le t\le \pi /2\right)$ about the y-axis.