Need some quick trigonometry help here! 2 * cos 10 / sin 20 equals to 1 / sin 10; But how do you derive one from the another? Thanks!

I will try my usual rule of not giving a direct answer but this case might be hard. I assume degrees rather than radians (not that it matters at this stage but I have seen such things end up in calculus territory). First stage: rearrange. I went for nothing as a denominator. Second stage: trigonometric identities. Rather sly use of one of the more rare identities today, the ones you want are sum formulas for sine and cosine . The one in question: sin (s + t) = sin s cos t + cos s sin t angle is 20 and nicely enough 10 + 10 equals 20 and 10 is the angle of choice in the other factors. Hopefully you can see where things go from here.