Question

Evaluate tan2a if tan a=-5/12, pi/2< a< pi

Answer 1

@jim_thompson5910

Answer 2

see page 2 of
http://tutorial.math.lamar.edu/pdf/Trig_Cheat_Sheet.pdf

You will use this identity
\[\Large \tan(2a) = \frac{2\tan(a)}{1-\tan^2(a)}\]

Answer 3

let me know if that is enough to get started

Answer 4

Would I start with 2tan(-5/12)/1-tan^2(-5/12)?

Answer 5

it's not tan(-5/12)

it's tan(a) = -5/12

Answer 6

so everywhere you see a "tan(a)", replace it with -5/12

Answer 7

\[\Large \tan(2a) = \frac{2\tan(a)}{1-\tan^2(a)}\]

\[\Large \tan(2a) = \frac{2*\left(-\frac{5}{12}\right)}{1-\left(-\frac{5}{12}\right)^2}\]

\[\Large \tan(2a) = ??\]

Answer 8

-120/119?

Answer 9

let me check

Answer 10

I'm getting the same result

Answer 11

Sweet. So that's the final answer?

Answer 12

yes it is

Answer 13

Thank you!!