Question

If `sinO=-4/5` and `O` is in `Q3`, find `cos2O`?

Answer 1

`-7/25`

Explanation:

#sin O = -4/5, then cos O = -3/5. using phytogoras theoram.

`cos 2 O = cos^2 O - sin^2 O`

`cos 2 O = (-3/5)^2 - (-4/5)^2`

`cos 2 O = (9/25) - (16/25) = -7/25`