# i want to explain the solution in this question

• Dec 7th 2009, 12:24 PM
r-soy
i want to explain the solution in this question
i want to explain the solution in this question ..
I worked a red line on the steps that I did not understood it
• Dec 7th 2009, 01:03 PM
masters
Quote:

Originally Posted by r-soy
i want to explain the solution in this question ..

I worked a red line on the steps that I did not understood it

Hi r-soy,

$\cos \frac{3\pi}{2}=0$

$\sin \frac{3\pi}{2}=-1$

Does that help?
• Dec 7th 2009, 01:42 PM
r-soy
Hi but from where we get
$
\cos \frac{2\pi}{2}
$

in step 2
• Dec 7th 2009, 01:51 PM
masters
Quote:

Originally Posted by r-soy
Hi but from where we get
$
\cos \frac{2\pi}{2}
$

in step 2

Looks like it might be a mistake to me. Should be $\cos \frac{3\pi}{2}$
• Dec 8th 2009, 06:27 AM
r-soy
thanks so much
• Dec 8th 2009, 06:47 AM
r-soy
ok who u can know

cos(3pi/2)=cos(270)=0
sin(3pi/2)=sin(270)= -1

from where i can get 0 and -1 ?

give me a way to finid them
• Dec 8th 2009, 08:22 AM
masters
Quote:

Originally Posted by r-soy
ok who u can know

cos(3pi/2)=cos(270)=0
sin(3pi/2)=sin(270)= -1

from where i can get 0 and -1 ?

give me a way to finid them

On your unit circle, at an angle of 270 deg or 3pi/2, the coordinates of the intersection of the circle with the negative side of the y-axis is (0, -1). Cosine is defined as x/r, where x = x-coordinate of the circle and r = the radius.

$\cos 270=\frac{x}{r}=\frac{-1}{1}=-1$

Similarly, sine 270 is defined as y/r.

$\sin 270=\frac{y}{r}=\frac{0}{1}=0$

Print this image and study it: Unit Circle