Question

If${\sum }_{i-l}^{20}si{n}^{-1}{x}_i=10\pi$, then ${\sum }_{i-l}^{20}{x}_i$ is equal to

• A. 20
• B. 10
• C. 11
• D. 21

Answer 1

The correct option is A

20

Since, $-\frac{\pi }{2}\le si{n}^{-1}{x}_i\le \frac{\pi }{2},\therefore si{n}^{-1}{x}_i=\frac{\pi }{2},1\le i\le 20$
$\therefore x_i=1,1\le i\le 20$. Thus ${\sum }_{i-l}^{20}{x}_i=20$