Now that I've got the first value, how do I find the second? All I know is that the CAST rule may be involved, but I don't know how to apply it in this situation. Help on this would be greatly appreciated.

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- Jun 8th 2010, 04:27 PMRogueDemonFind the two possible values of theta

Now that I've got the first value, how do I find the second? All I know is that the CAST rule may be involved, but I don't know how to apply it in this situation. Help on this would be greatly appreciated. - Jun 8th 2010, 04:36 PMundefined
- Jun 8th 2010, 04:43 PMRogueDemon
Thanks very much for the response. Just wondering though, why is it

*360*- 121 as opposed to something like 180 - 121? Is it because this question involves cos, where cos covers the 360 degree region of the circle and sin covers the 180 degree region? - Jun 8th 2010, 04:54 PMundefined
Actually it's because cos(x) is an even function, meaning cos(x) = cos(-x). It just so happens that cos(-x) = cos(360 - x). I figured you were probably looking for an answer in the range [0, 360], so I gave the latter answer.

The corresponding identity for sin(x) is sin(x) = -sin(-x) because sin(x) is odd.

It is also true that sin(x) = sin(180-x) but this more closely corresponds with cos(x) = -cos(180-x). See here.