Determine the corresponding ordered pair of the point on the unit circle for the following angle: -390°

Question

Choices are ; 

 

(- sqrt 3/2, -1/2)

 

( sqrt 3/2, 1/2)

 

( sqrt 3/2, -1/2)

 

( - sqrt 3/2, 1/2)
 

Answer 1

Hello Sheily,

 

If we keep in mind that 360 degrees around the unit circle is one complete revolution, we know that although the angle is bigger, we still have a reference triangle from the unit circle.

 

We can add 360 to the -390 to find that we are looking at a -30 degree reference angle. This correlates to a 30/60/90 right triangle in the 4th quadrant. 

 

Knowing this and recognizing the quadrant we are in (for the correct "signs" of the coordinate), we can determine the correct ordered pair.