SOLUTION: Find the exact value of the given trigonometric function. Do not use a calculator cos 9pi/4 I need to determine the angle that equals 9pi/4 when added to 2pi The answer is pi/4

Question 284047: Find the exact value of the given trigonometric function. Do not use a calculator
cos 9pi/4
I need to determine the angle that equals 9pi/4 when added to 2pi
The answer is pi/4 but I can not figure out how that is.
Thank you
Found 2 solutions by solver91311, jim_thompson5910:
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!

Here's a hint:

So,

John

Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Let x = unknown angle

Since adding radians to 'x' radians gets us radians, this means that

Start with the given equation.

Subtract from both sides.

Multiply by

Combine the fractions.

Subtract.

So if you add radians to radians, you will get radians.
RELATED QUESTIONS
Use the fact that the trigonometric functions are periodic to find the exact value of... (answered by stanbon)
Use the fact that the trigonometric functions are periodic to find the exact value of... (answered by Alan3354)
Use the fact that the trigonometric functions are periodic to find the exact value of... (answered by Alan3354)
Use the given information to determine the exact trigonometric value. If cos(theta)=4/5... (answered by stanbon)
find the exact value of the expression. do not use a calculator sin(-4pi) + cos... (answered by lwsshak3)
Rewrite the expression as the sine, cosine, or tangent of a double-angle.... (answered by greenestamps)
Find the exact value of the expression. Do not use a calculator. Cos^-1[cos(-5pi/4)].... (answered by stanbon)
find the exact value of tan... (answered by Fombitz)
Given that theta is an acute angle and sin(theta) = 17/37, find the exact value of... (answered by KMST)