Answer:
We know that, for a right triangle:
Cos(A) = (adjacent cathetus)/hipotenuse
sin(A) = (opposite cathetus)/Hipotenuse.
If we are in a right triangle inside the unit circle, we have that hypotenuse = 1.
Now, when you draw the unit circle, now from the center of the axis you must draw a straigth line (that forms an angle of 120° with the x-axis), and in the point where it cuts the unit circle we do 2 things.
from this point, you can draw a parallel line to the y-axis, the point where this line touches the x-axis is the value of the cosine.
Now you draw a line that is parallel to the x-axis (remember that the line must pass trough the point of before), the point where this line cuts the y-axis is the value of the sine
You should get:
sin(120°) = 0.87
cos(120°) = -0.5
