Question

为什么sin(π/3+c)=1/2,0＜c＜π,所以π/3+c=5π/6

Answer 1

0＜c＜π

则

π/3< π/3+c < 4π/3

设角度为a = π/3+c

在该角度范围（π/3,4π/3）内使得sin(a)=1/2的只有5π/6

所以a = 5π/6 = π/3+c