I was wondering why cos(3pie/4) = cos(-3pie/4)?

I know 3pie/4 is 135 degrees so in 2nd Quad, where only sin is positive.

But how do I know it is equal to cos(-3pie/4)?

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- Oct 28th 2006, 08:02 AMclassicstringsOne more quick question!
I was wondering why cos(3pie/4) = cos(-3pie/4)?

I know 3pie/4 is 135 degrees so in 2nd Quad, where only sin is positive.

But how do I know it is equal to cos(-3pie/4)? - Oct 28th 2006, 08:07 AMCaptainBlack
- Oct 28th 2006, 08:19 AMclassicstrings
Ok, is this the same as sin? (tan?) Thanks

- Oct 28th 2006, 08:35 AMCaptainBlack
- Oct 28th 2006, 08:37 AMAglaia
use this trick: keep in your mind the gognometric circonference; then usinig radians, divide it in the slices you need...you will soon notice that moving clockwise or counterclockwise you'll get to the same point..it's not what you can define a math proof, but it can help you understand...now you should be able to answer to your question about sin and tan