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

Algebra ->  Trigonometry-basics -> 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       Log On


   

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) About Me  (Show Source):
You can put this solution on YOUR website!


Here's a hint:



So,




John

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

Since adding 2pi radians to 'x' radians gets us 9pi%2F4 radians, this means that x%2B2pi=9pi%2F4


x%2B2pi=9pi%2F4 Start with the given equation.


x=9pi%2F4-2pi Subtract 2pi from both sides.


x=9pi%2F4-8pi%2F4 Multiply 2pi by 4%2F4


x=%289pi-8pi%29%2F4 Combine the fractions.


x=pi%2F4 Subtract.


So if you add 2pi radians to pi%2F4 radians, you will get 9pi%2F4 radians.