Question

Найти определенный интеграл (верх.п/2; ниж.0) cos^2*((п/6)-x)*dx оч оч заранее !

Answer 1

$\int\limits^{\frac{\pi}{2}}_0 {cos^2(\frac{\pi}{6}-x)} \, dx = \int\limits^{\frac{\pi}{2}}_0 {\frac{1+sin2(\frac{\pi}{6}-x)}{2}} \, dx = \frac{1}{2} \int\limits^{\frac{\pi}{2}}_0 \, dx + \frac{1}{2} \int\limits^{\frac{\pi}{2}}_0 {sin(\frac{\pi}{3}-2x)} \, dx =$

$= \frac{1}{2} \int\limits^{\frac{\pi}{2}}_0 \, dx - \frac{1}{4} \int\limits^{\frac{\pi}{2}}_0 {sin(\frac{\pi}{3}-2x)} \, d(\frac{\pi}{3}-2x) = \frac{1}{2}x|^{\frac{\pi}{2}}_0 + \frac{1}{4}cos(\frac{\pi}{3}-2x)|^{\frac{\pi}{2}}_0 =$

$= \frac{1}{2}\cdot\frac{\pi}{2} + \frac{1}{4}cos(\frac{\pi}{3}-2\cdot\frac{\pi}{2}) - \frac{1}{4}cos\frac{\pi}{3} = \frac{\pi}{4} + \frac{1}{4}cos(\pi-\frac{\pi}{3}) - \frac{1}{4}\cdot\frac{1}{2} =$

$= \frac{\pi}{4} - \frac{1}{4}cos\frac{\pi}{3} - \frac{1}{8} = \frac{\pi}{4} - \frac{1}{4}\cdot\frac{1}{2} - \frac{1}{8} = \frac{\pi}{4} -\frac{1}{8} - \frac{1}{8} = \frac{\pi}{4} -\frac{1}{4}$