Đáp án
Ta có:
cos (-2500) = cos 2500 = cos (1800 + 700) = -cos 700
= - cos (900 – 200) = -sin 200 ≈ 0, 342
sin 5200 = sin (3600 + 1600) = sin 1600
= sin (1800 – 200) = sin 200 ≈ 0, 342
\(\sin {{11\pi } \over {10}} = \sin (\pi + {\pi \over {10}}) \)
\(= - \sin {\pi \over {10}} = - \sin {\pi \over {10}} = - \sin {18^0} \approx 0,309\)
