Question

1/2sin²c=

求该题演算过程
设a=1/2COS6°-√3/2sin6°,b=2tan13°/1+tan13°,c=√1-cos50°/2,则有
A,a＜b＜c B,a＞b＞c C,a＜c＜b D,b＜c＜a

Answer 1

a=1/2cos6°-√3/2sin6°=sin30°cos6°-cos30°sin6°=sin(30°-6°)=sin24°
b=2tan13°/(1+tan13°)=tan26°
cos50°=cos2×25°=1-2sin²25°
c=√[(1-cos50°)/2]=sin25°
a