How do you figure out the sin,cos,tan of equations such as 3 pi/4 without using calculator? I'm so confused. I know the answer for the sin of 3 pi/4 is negative root 2 over 2, but what are the steps to get those answers?

Question

campbell_st · Answer

well you can put your calculator into radian mode rather than degree mode. 

or use the fact 

$$180^o = \pi$$

so find 

$$\frac{3}{4} \times 180 = 135^o$$

so this is a 2nd quadrant angle, where sine is positive. 

so the answer is 

$$\sin(\frac{3\pi}{4}) = \sin(135) = \sin(45) = \frac{\sqrt{2}}{2}$$

hope it helps

anonymous · Answer

This clears it up a little bit and makes me understand it easier since my teacher just runs through problems instead of going step by step. Thank you so much!!!

wolf1728 · Answer

There's a handy chart on this page: http://1728.org/degrees.htm that shows the PI value every 15° through 360°