Find tan2A when tanA = 1/3 and π<A<3π/2.

Question

A) 4/5

B) 5/4

C) 3/4

D) 3/5

Answer 1

So A in in quadrant III
tan 2A = 2tanA/(1 - tan^2 A)
= 2(1/3)/(1 - 1/9)
= (2/3) / (8/9)
= (2/3)(9/8)
= 18/24 = 3/4