Question

What is the exact value of cos(2 x) if tan( x) =
-3/4 and x is in quadrant IV?

Answer 1

-1/2

Answer 2

how did you come up wit that?

Answer 3

1+tan^2 x = sec^2 x
have you seen this formula?

Answer 4

no I havent

Answer 5

K there are three trigonometric identities this is one of them. Can you solve it now?

Answer 6

also I think -1/2 is not the correct answer. As it is in 4th quad cos is always +ve

Answer 7

there is this direct formula which you can use cos 2x = (1 - tan^2 x) / (1 + tan^2 x)

Answer 8

from the triangle in 4th quadrant
you can get sin and cos
\[\sin x = -\frac{3}{5}\]
\[\cos x = \frac{4}{5}\]
the double angle identity is:
\[\cos 2x = \cos^2 x - \sin^2 x\]

Answer 9

ok so cos is 3/2?

Answer 10

wait no im lost

Answer 11

cos is always between +1 and -1 lol

Answer 12

cos2x = 16/25-9/25

Answer 13

7/25= cos2x?