# Thread: math 12 - unit circle intersection?

1. ## math 12 - unit circle intersection?

Point A (-5,-2) lies on the terminal arm of angle (theta) in Standard Position. Point P is the point of intersection of the terminal arm of (Theta) and the unit circle centred at (0,0) Determine the y- coordinate of point p.

It seems like there some information missing but im possitive its all there i cant figure this one out..

2. Originally Posted by bene
Point A (-5,-2) lies on the terminal arm of angle (theta) in Standard Position. Point P is the point of intersection of the terminal arm of (Theta) and the unit circle centred at (0,0) Determine the y- coordinate of point p.

It seems like there some information missing but im possitive its all there i cant figure this one out..

First find the terminal angle for point A.

Then sketch the unit circle.

Sketch, on the unit circle, the terminal angle for A. This give you point P. And, of course, the unit circle has a radius of 1.

-Dan

3. so the angle is tan-(5/2) = 68.2?

then make a trangle with hypotenuse(radius) 1 and the angle 68.2 which would give the horizontal component .93?

thanks

4. Originally Posted by bene
so the angle is tan-(5/2) = 68.2?

then make a trangle with hypotenuse(radius) 1 and the angle 68.2 which would give the horizontal component .93?

thanks
What this boils down to is finding $\displaystyle sin \left [ tan^{-1} \left ( \frac{-2}{-5} \right ) \right ] \approx -0.371391$
(Negative since we are in QIII.) You appear to have your x and y's mixed up.

-Dan

5. yeah x and y was backwards

anyways thanks a lot!!