Here, maybe this can help you. Remember the 30 60 90 degree triangle. These can be used to find the sines, cosines and tangents of 30, 60, 120, 150, 210, 240, 300, and 330. Look at the diagram. Just remember that the large angle that isn't the 90 degree angle, is the 60 degree angle, and the short one is the 30 degree angle. Using this diagram, you can easily find where the angles stand at. For instance, in the left diagram, the angle at the top left (the one pointing up and to the right) is 60 degree's before the 180 degree line, therefore its angle is 180 - 60 or 120. The sine = opposite over hypotenuse, or vertical height over hypotenuse. So the sine of 120 = sqrt (3) / 2.

Notice the vertical height is negative when it falls below the origin, and the horizontal lengths are negative when they are to the left of the origin. But the hypotenuse is always postive. Therefore, the cosine of 120 equals hypotenuse over adjacent, or hypotenuse over horizontal length. Here the horizontal length is -1, the hypotenuse is 2 (always positive) so the cosine is -1 over 2 or -1/2. Notice the angle below also has a cosine of -1 over 2.

In the first quadrant, sines, cosines and tangents are all positive. In the second, only sines are postive, in the third quadrant, only tangents are postive, and in the forth quadrant, only cosines are positive. You can use the mnemonic All Students Take Calculus to remember which trigonometric functions are positive in each quadrant. All in the first quadrant all trig functions are positive. Students, S for Sine, in the 2nd quadrant only sines arep positeve. Take, T for tangent, in the third quadrant only tangents are postive. Calculus. C for Cosine, in the 4th quadrant, only cosines are positive.

Hope this helps.