Giải bài 64 trang 30 sách bài tập toán 12 - Cánh diều
Tính: a) (intlimits_0^{frac{pi }{2}} {sin xdx} ); b) (intlimits_0^{frac{pi }{4}} {cos xdx} ); c) (intlimits_{frac{pi }{4}}^{frac{pi }{2}} {frac{1}{{{{sin }^2}x}}dx} ); d) (intlimits_0^{frac{pi }{4}} {frac{1}{{{{cos }^2}x}}dx} ); e) (intlimits_0^{frac{pi }{2}} {left( {sin x - 2} right)dx} ); g) (intlimits_0^{frac{pi }{4}} {left( {3cos x + 2} right)dx} ).
Đề bài
Tính:
a) \(\int\limits_0^{\frac{\pi }{2}} {\sin xdx} \);
b) \(\int\limits_0^{\frac{\pi }{4}} {\cos xdx} \);
c) \(\int\limits_{\frac{\pi }{4}}^{\frac{\pi }{2}} {\frac{1}{{{{\sin }^2}x}}dx} \);
d) \(\int\limits_0^{\frac{\pi }{4}} {\frac{1}{{{{\cos }^2}x}}dx} \);
e) \(\int\limits_0^{\frac{\pi }{2}} {\left( {\sin x - 2} \right)dx} \);
g) \(\int\limits_0^{\frac{\pi }{4}} {\left( {3\cos x + 2} \right)dx} \).
Phương pháp giải - Xem chi tiết
Sử dụng các công thức:
• \(\int {\sin xdx} = - \cos x + C\).
• \(\int {\cos xdx} = \sin x + C\).
• \(\int {\frac{1}{{{{\cos }^2}x}}dx} = \tan x + C\).
• \(\int {\frac{1}{{{{\sin }^2}x}}dx} = - \cot x + C\).
Lời giải chi tiết
a) \(\int\limits_0^{\frac{\pi }{2}} {\sin xdx} = \left. { - \cos x} \right|_0^{\frac{\pi }{2}} = - \cos \frac{\pi }{2} + \cos 0 = 1\).
b) \(\int\limits_0^{\frac{\pi }{4}} {\cos xdx} = \left. {\sin x} \right|_0^{\frac{\pi }{4}} = \sin \frac{\pi }{4} - \sin 0 = \frac{{\sqrt 2 }}{2}\).
c) \(\int\limits_{\frac{\pi }{4}}^{\frac{\pi }{2}} {\frac{1}{{{{\sin }^2}x}}dx} = \left. { - \cot x} \right|_{\frac{\pi }{4}}^{\frac{\pi }{2}} = - \cot \frac{\pi }{2} + \cot \frac{\pi }{4} = 1\).
d) \(\int\limits_0^{\frac{\pi }{4}} {\frac{1}{{{{\cos }^2}x}}dx} = \left. {\tan x} \right|_0^{\frac{\pi }{4}} = \tan \frac{\pi }{4} - \tan 0 = 1\).
e) \(\int\limits_0^{\frac{\pi }{2}} {\left( {\sin x - 2} \right)dx} = \left. {\left( { - \cos x - 2{\rm{x}}} \right)} \right|_0^{\frac{\pi }{2}} = \left( { - \cos \frac{\pi }{2} - 2.\frac{\pi }{2}} \right) - \left( { - \cos 0 - 2.0} \right) = 1 - \pi \).
g) \(\int\limits_0^{\frac{\pi }{4}} {\left( {3\cos x + 2} \right)dx} = \left. {\left( {3\sin x + 2{\rm{x}}} \right)} \right|_0^{\frac{\pi }{4}} = \left( {3\sin \frac{\pi }{4} + 2.\frac{\pi }{4}} \right) - \left( {3\sin 0 + 2.0} \right) = \frac{{3\sqrt 2 }}{2} + \frac{\pi }{2}\).