math 12 - unit circle intersection?

• Mar 2nd 2008, 06:55 PM
bene
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..

• Mar 2nd 2008, 07:05 PM
topsquark
Quote:

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
• Mar 2nd 2008, 07:26 PM
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
• Mar 2nd 2008, 08:02 PM
topsquark
Quote:

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

-Dan
• Mar 2nd 2008, 08:09 PM
bene
yeah x and y was backwards

anyways thanks a lot!!