sin(A/2)=1/4,求A
===>A/2=arcsin(1/4)
===>A=2arcsin(1/4)
或者,A=π-2arcsin(1/4).
A=π-2arcsin(1/4)?
sin(30°/2)≈0.26,sin((180°-30°)/2)≈0.97,不相等啊为什么呢