# Thread: find sine and cosine

1. ## find sine and cosine

Hi,

1)27pi/2

: sin (13pi + pi/2)
=1
so cos=0

2)11pi/2

:sin(5pi + pi/2)
=1
so cos=0

i used the unit circle to figure this out

Thanks

2. Originally Posted by smmmc
Hi,

1)27pi/2

: sin (13pi + pi/2)
=1
so cos=0

2)11pi/2

:sin(5pi + pi/2)
=1
so cos=0

i used the unit circle to figure this out

Thanks
What you've posted is a lot of nonsense.

$\displaystyle \sin$ is meaningless unless it is written as the sine of an angle.

So is $\displaystyle \cos$.

3. $\displaystyle \sin\left(13\pi+\frac{\pi}{2}\right)=\sin\left(12\ pi+\pi+\frac{\pi}{2}\right)=$

$\displaystyle =\sin\left(\pi+\frac{\pi}{2}\right)=-\sin\frac{\pi}{2}=-1$

Similarly, $\displaystyle \sin\left(5\pi+\frac{\pi}{2}\right)=-1$

4. Thank You Red Dog.

5. Originally Posted by Prove It
What you've posted is a lot of nonsense.

$\displaystyle \sin$ is meaningless unless it is written as the sine of an angle.

So is $\displaystyle \cos$.
What you've written is non-sense. Sine and cosine are often used in mathematics in ways that have nothing to do with angles.

Sine and cosine are commonly introduced in basic trigonometry courses but you should have learned other definitions, that, again, have nothing to do with angles, in, say, secondary school.

6. Can you explain it more halls?

thx