Question

Find tan2A when cosA = -3/5 and π/2 12 years ago

Answer 1

use right triangle to find sinA and tanA

sinA = 4/5
tanA = -4/3

now use double angle identity to find tan(2A)
\[\tan (2A) = \frac{2\tan A}{1-\tan^{2} A}\]
plug in -4/3 for tanA