Question

Find tan2A when cosA = -3/5 and π/2 13 years ago

Answer 1

Are you sure that it's tan2A and not tanA?

Answer 2

Yes I'm sure it's tan2A.

Answer 3

Okay. Well the \[\tan \theta = \frac{ \sin \theta }{ \cos \theta }\]

Answer 4

Since you know the cos of A is \[\frac{ -3 }{ 5}\] the sine is of A is the reciprocal of cosine: \[\frac{ -5 }{ 3 }\]

Answer 5

the double angle identity for tan is:
\[\large \tan(2x) = \frac{2 \tan (x)}{1 - \tan^2 (x)}\]

Since we know that cos(x) is -3/5 and sin(x) is 5/3 (since it is in the second quadrant, sine is positive), we can replace tan(x) with sin(x) and cos(x).

Can you do it from here?

Answer 6

sin(x) =5/3 !!?!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Answer 7

you can't have Sin A = -5/3 ... its impossible... since the range of sin(x) is -1<= x<= 1

Answer 8

sin A would be 4/5

Answer 9

draw a triangle



find x by pythagoras then you'll know sin A

please... sin A -5/3 wow

Answer 10

yeah, my bad...