What are the coordinates of the terminal point corresponding to = –120? Use the Pythagorean theorem to prove that this point lies on the unit circle?
Accepted Solution
A:
we know that the unit circle has a radius equals 1 unit
-120°------> is an angle belong to the III quadrant so the x and y coordinates will be negative x=r*cos ∅ y=r*sin ∅ where r=1 and ∅=180-120-----> ∅=60°
therefore x=(1)*cos 60°-----> x=1/2-----> x=-1/2 (remember x is negative) y=(1)*sin 60°-----> y=√3/2-----> y=-√3/2 (remember y is negative
let's apply the Pythagorean theorem x²+y²-----> (-1/2)²+(-√3/2)²----> (1/4)+(3/4)-----> 1----> is ok because 1 is the radius of the unit circle
the answer is the coordinates of the terminal point are (-1/2,-√3/2)