cos(40)+cos(80)+cos(100)+cos(120)+cos(140)

解答

cos (4 0^{\circ}) + cos (8 0^{\circ}) + cos (10 0^{\circ}) + cos (12 0^{\circ}) + cos (14 0^{\circ})

- 0.5

求解步骤

cos (4 0^{\circ}) + cos (8 0^{\circ}) + cos (10 0^{\circ}) + cos (12 0^{\circ}) + cos (14 0^{\circ})

整理为小数形式

= - 0.5

2 sin (5 0^{\circ}) cos (5 0^{\circ})

arcsinh (\frac{1}{2})

csc (\frac{2 π}{3}) - cos (\frac{5 π}{4}) + sin (\frac{π}{6})

sin (arccos (- \frac{9}{145}))

\frac{1}{cos ( 9 0 ^{\circ} )}