一, 三角函数
正弦sin(a) = b / c
余弦cos(a) = a / c
tan(a) = b / a
csc(a) = 1 / sin(a) = c / b
sec(a) = 1 / cos(a) = c / a
cot(a) = 1 / tan(a) = a / b
常用的三角函数函数值表
| a (Degrees) | a (Radians) | sin a | cos a | tan a |
| 0 | 0 | 0 | 1 | 0 |
| 30 | PI / 6 | 0.5 | 0.8660 | 0.5774 |
| 45 | PI / 4 | 0.7071 | 0.7071 | 1 |
| 60 | PI / 3 | 0.8660 | 0.5 | 1.7321 |
| 90 | PI / 2 | 1 | 0 | ----- |
| 120 | 2*PI/3 | 0.8660 | -0.5 | -1.7321 |
| 180 | PI | 0 | -1 | 0 |
| 270 | 3*PI/2 | -1 | 0 | ----- |
| 360 | 0 | 0 | 1 | 0 |
正弦函数曲线
余弦函数曲线
二, 三角代数
由单位圆 x2 + y2 = 1来推导
sin2a + cos2a = 1
sin(-a) = -sin(a)
cos(-a) = cos(a)
tan(-a) = -tan(a)
sin(a1 + a2) = sin(a1) * cos(a2) + cos(a1) * sin(a2)
sin(a1 - a2) = sin(a1) * cos(a2) - cos(a1) * sin(a2)
cos(a1 + a2) = cos(a1) * cos(a2) - sin(a1) * sin(a2)
cos(a1 - a2) = cos(a1) * cos(a2) + sin(a1) * sin(a2)
原文:http://www.cnblogs.com/HelloCG/
