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)?
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