# Thread: i want to explain the solution in this question

1. ## 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

2. 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,

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

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

Does that help?

3. Hi but from where we get
$\displaystyle \cos \frac{2\pi}{2}$
in step 2

4. Originally Posted by r-soy
Hi but from where we get
$\displaystyle \cos \frac{2\pi}{2}$
in step 2
Looks like it might be a mistake to me. Should be $\displaystyle \cos \frac{3\pi}{2}$

5. thanks so much

6. 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

7. 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.

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

Similarly, sine 270 is defined as y/r.

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

Print this image and study it: Unit Circle