Chapter 4 - Integration - Review Exercises - Page 314: 89

$$\eqalign{ & {\text{Trapezoidal Rule}} \approx 0.6365 \cr & {\text{Simpson's Rule}} \approx 0.6847 \cr & {\text{Graphing utility}} \approx 0.7040 \cr} $$

$$\eqalign{ & \int_0^{\pi /2} {\sqrt x \cos x} dx \cr & {\text{For }}n = 4,{\text{ }}\Delta x = \frac{{b - a}}{n} = \frac{{\pi /2 - 0}}{4} = \frac{\pi }{8},{\text{ then,}} \cr & {x_0} = 0,{\text{ }}{x_1} = \frac{\pi }{8},{\text{ }}{x_2} = \frac{\pi }{4},{\text{ }}{x_3} = \frac{{3\pi }}{8},{\text{ }}{x_4} = \frac{\pi }{2} \cr & \cr & {\text{*Using the trapezoidal Rule }}\left( {{\text{THEOREM 4}}{\text{.17}}} \right) \cr & \int_a^b {f\left( x \right)} dx \approx \frac{{b - a}}{{2n}}\left[ {f\left( {{x_0}} \right) + 2f\left( {{x_1}} \right) + \cdots 2f\left( {{x_{n - 1}}} \right) + f\left( {{x_n}} \right)} \right] \cr & \int_0^{\pi /2} {\sqrt x \cos x} dx \approx \frac{\pi }{{2\left( 8 \right)}}\left[ {f\left( 0 \right) + 2f\left( {\frac{\pi }{8}} \right) + 2f\left( {\frac{\pi }{4}} \right)} \right] \cr & + \frac{\pi }{{2\left( 8 \right)}}\left[ {2f\left( {\frac{{3\pi }}{8}} \right) + f\left( {\frac{\pi }{2}} \right)} \right] \cr & \int_0^{\pi /2} {\sqrt x \cos x} dx \approx \frac{\pi }{{16}}\left[ {0 + 2\sqrt {\frac{\pi }{8}} \cos \left( {\frac{\pi }{8}} \right) + 2\sqrt {\frac{\pi }{4}} \cos \left( {\frac{\pi }{4}} \right)} \right] \cr & {\text{ }} + \frac{\pi }{{16}}\left[ {2\sqrt {\frac{{3\pi }}{8}} \cos \left( {\frac{{3\pi }}{8}} \right) + \sqrt {\frac{\pi }{2}} \cos \left( {\frac{\pi }{2}} \right)} \right] \cr & {\text{Simplifying}} \cr & \int_0^{\pi /2} {\sqrt x \cos x} dx \approx 0.6365 \cr & \cr & {\text{*Using Simpson's Rule }}\left( {{\text{THEOREM 4}}{\text{.19}}} \right) \cr & \int_a^b {f\left( x \right)} dx \approx \frac{{b - a}}{{3n}}\left[ {f\left( {{x_0}} \right) + 4f\left( {{x_1}} \right) + 2f\left( {{x_2}} \right) + 4f\left( {{x_3}} \right) + \cdots } \right. \cr & \left. {{\text{ }} + 4f\left( {{x_{n - 1}}} \right) + f\left( {{x_n}} \right)} \right] \cr & \int_0^{\pi /2} {\sqrt x \cos x} dx \approx \frac{\pi }{{24}}\left[ {0 + 4\sqrt {\frac{\pi }{8}} \cos \left( {\frac{\pi }{8}} \right) + 2\sqrt {\frac{\pi }{4}} \cos \left( {\frac{\pi }{4}} \right)} \right] \cr & {\text{ }} + \frac{\pi }{{24}}\left[ {4\sqrt {\frac{{3\pi }}{8}} \cos \left( {\frac{{3\pi }}{8}} \right) + \sqrt {\frac{\pi }{2}} \cos \left( {\frac{\pi }{2}} \right)} \right] \cr & {\text{Simplifying}} \cr & \int_0^{\pi /2} {\sqrt x \cos x} dx \approx 0.6847 \cr & {\text{Simplifying}} \cr & \int_2^3 {\frac{2}{{1 + {x^2}}}} dx \approx 0.1661 \cr & \cr & {\text{Using a graphing utility we obtain}} \cr & \int_0^{\pi /2} {\sqrt x \cos x} dx \approx 0.7040 \cr} $$