Monday

October 20, 2014

October 20, 2014

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

find the exact value. Do not use a calculator

cos 7pi

- Calculus (trig stuff) -
**michael**, Monday, October 26, 2009 at 12:24am2&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

**Answer this Question**

**Related Questions**

math - Eliminate the parameter (What does that mean?) and write a rectangular ...

Trigonometry - How do you find the exact value of cos -7pi/12 without using a ...

Trigonometry - Hi, I need help with this question: Use the addition and ...

trig - Evaluate giving exact values and identities. Calculator based solutions ...

trig - Find the exact value. Without using a calculator a) cos (-17pi/6) b) sec...

math - Determine the exact value of cos^-1 (pi/2). Give a number and an ...

Trig - If cosx = 10/19 an pi < x < 2pi, find the exact value of cos x/2 ...

trig - 2sin(x)cos(x)+cos(x)=0 I'm looking for exact value solutions in [0, 3&#...

Math- Trig - 1. Determine the exact value of cos^-1 (pi/2). Give number and ...

Pre Calculus - ok I appologize for my stupidity... I'll answer your question... ...