given cos theta is equal to - 4/ 7 then we can conclude that theta is in the second and third quadrants. In this case, the other leg is equal to square root of (7^2 - 4^2 ) equal to square root of 33. In this case, sin theta can be equal to +- square root of 33 / 7 and tan theta is equal to +-square root of 33 / 4.
