Posted by **Calculus (trig stuff)** on Sunday, October 25, 2009 at 9:33pm.

How do I do these type of problems

find the exact value. Do not use a calculator

cos 7pi

- Calculus (trig stuff) -
**michael**, Monday, October 26, 2009 at 12:24am
2&pi is one full rotation around the circle, so you can think of 2&pi as being the same as 0. so 7 pi is the same as going around the circle 3 full times with 1&pi left over, to figure this out exactly you can do the following:

(7/2) = 3 +1/2

the 3 is how many times we went 2&pi around the circle, and what we have left is (1/2)*2&pi or 1&pi

cos(&pi) = -1

To do another example

sin((9/2)&pi)

well (9/2)/2 is the same as (9/2)*(1/2)=(9/4)

we get 2 + 1/4 so we get 2 full rotations plus 1/4 of a full rotation. A full rotation is just 2&pi so:

2&pi*(1/4) = &pi/2

sin(&pi/2) = 1

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