Sine and Cosine Functions

[Guest]

Suppose I have a problem like this:

cos(-7pie/3) = ?

? = 1/2

Is there a faster method of solving problems like these, rather than converting to degrees, drawing a quick circle to find the type of triangle, etc.

Basically, is there a formula without giving an answer in a decimal? Thanks

 

[nezenic]

For the trigonometric functions with the more common and simple arguments, I visualize the unit circle and can figure out the answer within a second or two without converting anything or writing anything down. The really common ones I memorized a while ago.