python cos_Python cos(90)和cos(270)不是0

到底是怎么回事？？

测试sin和cos函数,找出为什么在将坐标输出到SVG文件时,我在错误的位置上获得如此美妙的定位.所以我制作了这个测试代码,我可以预测答案是找出原因.奇怪的是,没有任何影响计算的东西会增加这种行为,而只是我将要留下的位置.如果位置为0并且在计算后将变为0,则它​​将不起作用,但如果position为1并且在计算之后它将变为1,则它起作用.

第一次测试：

import math

cX = 2

cY = 2

r = 2

rcX = cX + (r * math.cos(math.radians(0)))

rcY = cY + (r * math.sin(math.radians(0)))

print rcX #4

print rcY #2

r = 1

rlX = rcX + (r * math.cos(math.radians(90)))

rlY = rcY + (r * math.sin(math.radians(90)))

print rlX #4

print rlY #3

r = 4

flX = rlX + (r * math.cos(math.radians(180)))

flY = rlY + (r * math.sin(math.radians(180)))

print flX #0

print flY #3

r = 2

print r * math.cos(math.radians(270))

print flX + (r * math.cos(math.radians(270))) #-3.67394039744e-16 should be 0

print flY + (r * math.sin(math.radians(270))) #1

现在我将cX更改为3,即使它不影响计算,它也能正常工作：

r * math.cos(math.radians(270))

该计算的结果将添加到x坐标

import math

cX = 3

cY = 2

r = 2

rcX = cX + (r * math.cos(math.radians(0)))

rcY = cY + (r * math.sin(math.radians(0)))

print rcX #5

print rcY #2

r = 1

rlX = rcX + (r * math.cos(math.radians(90)))

rlY = rcY + (r * math.sin(math.radians(90)))

print rlX #5

print rlY #3

r = 4

flX = rlX + (r * math.cos(math.radians(180)))

flY = rlY + (r * math.sin(math.radians(180)))

print flX #1

print flY #3

r = 2

print r * math.cos(math.radians(270))

print flX + (r * math.cos(math.radians(270))) #1

print flY + (r * math.sin(math.radians(270))) #1