Question

Prove that.....Tan 70 = tan 20 + 2 tan 50...

Answer 1

tan (70)=tan (20+50)
=(tan50+tan20)/(1-tan20.tan50)
we know
tan20 =cot70=1/tan70
use this
tan70=(tan50+tan20)/(1-1/tan70.tan50)
=(tan50 +tan20)/{(tan70-tan50)/tan70}

tan70=tan70 (tan50+tan20)/(tan70-tan50)

1=(tan50+tan20)/(tan70-tan50)

tan70-tan50=tan50+tan20

tan70=tan20+2tan50