1/sin10°-根号3/sin80°

题目

1/sin10°-根号3/sin80°
原式=1/sin10-√3/cos10
=(cos10-√3sin10)/sin10cos10
=2(1/2cos10-√3/2*sin10)/sin10cos10
=2cos(10+60)/sin10cos10
=4cos70/sin20
=4请将=2(1/2cos10-√3/2*sin10)/sin10cos10
=2cos(10+60)/sin10cos10
写的更细些不明白2cos(10+60哪来的

答案

原式=1/sin10-√3/cos10 =(cos10-√3sin10)/sin10cos10 =2(1/2cos10-√3/2*sin10)/sin10cos10 =2(cos60cos10-sin60sin10))/sin10cos10 =2cos(10+60)/sin10cos10 =4cos70/sin20