1/sin(120-a)+1/sin(120+a)=4/√3
√3[sin(120-a)+sin(120+a)]=sin(120-a)*sin(120+a)
2√3sin120cosa=1/2[cos2a-cos240]
6cosa=cos2a+cos60
2cos2a-12cosa+1=0
2cos^2a-12cosa-1=0
cosa=3-√10
1/sin(120-a)+1/sin(120+a)=4/√3
√3[sin(120-a)+sin(120+a)]=sin(120-a)*sin(120+a)
2√3sin120cosa=1/2[cos2a-cos240]
6cosa=cos2a+cos60
2cos2a-12cosa+1=0
2cos^2a-12cosa-1=0
cosa=3-√10