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
1
30
PI / 6
0.5
0.8660
0.5774
45
PI / 4
0.7071
60
PI / 3
1.7321
90
PI / 2
-----
120
2*PI/3
-0.5
-1.7321
180
PI
-1
270
3*PI/2
360
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/
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