Question

tan 20° tan 40° tan 80° = 13 how to solve this? ​

Answer 1

tan20° tan40° tan80°

= tan20° tan(60° - 20°) tan(60° + 20°)

= tan(3×20°)

... $tan \theta. tan(60° - \theta). tan(60° + \theta) = tan 3\theta$

= tan60°

= $\sqrt{3}$