Mathematics
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OpenStudy (anonymous):
what is sin (-13pi/4)
what is sin (-13pi/4)
@Mathematics

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OpenStudy (anonymous):
tyler can you help me with these two pls cos (
cos (5pi/3)
cos(-270 degrees)
and please show work

OpenStudy (anonymous):
I can help you with the first one.

OpenStudy (anonymous):
First, change \[- \frac{13 \pi}{4} \] into degrees to make things easy.

OpenStudy (anonymous):
Do you know how to do that?

OpenStudy (anonymous):
is it -13/4 times 180

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OpenStudy (anonymous):
Almost

OpenStudy (anonymous):
\[- \frac{13 \pi}{4} * \frac{180}{\pi}\]

OpenStudy (anonymous):
so we get -585 degrees?

OpenStudy (anonymous):
So essentially yes because the pi's cancel.

OpenStudy (anonymous):
Correct

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OpenStudy (anonymous):
ok what do we do with the degree

OpenStudy (anonymous):
-585 is more than one revolution. So we can add a revolution (or 360 degrees) to -585

OpenStudy (anonymous):
-585 + 360 = ?

OpenStudy (anonymous):
-225

OpenStudy (anonymous):
Good.

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OpenStudy (anonymous):
Now i like to deal with positive degrees. So to turn -225 into positive degrees. You do this \[-225 + 360\] Which is what?

OpenStudy (anonymous):
135

OpenStudy (anonymous):
Ok so saying \[\sin(- \frac{13\pi}{4})\] is like saying \[\sin(135)\] which is much easier to work with.

OpenStudy (anonymous):
so thats the final answer, 135?

OpenStudy (anonymous):
Well what is sin(135) ?

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OpenStudy (anonymous):
sqrt2/2

OpenStudy (anonymous):
Correct!

OpenStudy (anonymous):
awesome, why cant you help me with the other two...you explain better than my teacher lol

OpenStudy (anonymous):
I can.. i wanted to start with the first one lol

OpenStudy (anonymous):
ok kool

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OpenStudy (anonymous):
so for cos(5pi/3) we convert to degrees first right

OpenStudy (anonymous):
ok so lets do \[\cos (\frac{5\pi}{3})\]

OpenStudy (anonymous):
and get 300 degrees

OpenStudy (anonymous):
Ok good.

OpenStudy (anonymous):
do i do any subtraction...not sure

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OpenStudy (anonymous):
Well, you can.

OpenStudy (anonymous):
so do i use 180 or 360

OpenStudy (anonymous):
You should know what sin cos and tan of pi/3, pi/4 and pi/6 are.

OpenStudy (anonymous):
So 300 is in the 4 th quadrant and you want a angle in the first so subtract 300 from 360

OpenStudy (anonymous):
So \[\cos(300) = \cos(60)\]

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OpenStudy (anonymous):
and cos(60) is 1/2?

OpenStudy (anonymous):
Now what is cos (60)? or pi/3

OpenStudy (anonymous):
1/2?

OpenStudy (anonymous):
Correct its 1/2

OpenStudy (anonymous):
good stuff man

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OpenStudy (anonymous):
cos(-270) we add 360 and get 90 and cos 90 is 0?

OpenStudy (anonymous):
now \[\cos(-270)\]

OpenStudy (anonymous):
You got it!! You got the hang of it now!! :)

OpenStudy (anonymous):
yeah thanks very much for the help

OpenStudy (anonymous):
No problem.

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OpenStudy (anonymous):
ok i have another one
Find sin of angle if sin of angle < 0 and cos of angle = 2/3

OpenStudy (anonymous):
1 and 4

OpenStudy (anonymous):
ok

OpenStudy (anonymous):
what do you mean

OpenStudy (anonymous):
i see how the amplitude is one

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OpenStudy (anonymous):
how do i find the period