proof left as an exercise

[Albert Chan]

Top-down proof (equivalent to previous post)

2*cos(30°) / (1+4*sin(70°))
= cos(30°) / (sin(30°) + 2*cos(20°))
= sin(20°)*cos(30°) / (sin(20°)*sin(30°) + sin(40°))
= sin(20°)*cos(30°) / (sin(20°)*sin(30°) + cos(50°))
= sin(20°)*cos(30°) / (cos(20°)*cos(30°))
= tan(20°)