The unit circle is represented below:
As can be observed in the figure above, for an angle (t), the relation between the trigonometric functions and x and y components is:
x = cos(t)
y = sen(t)
x is positive in the first and in the fourth quadrant. Thus, cos (t) will be positive for angles in the first and fourth quadrant.
y is positive in the first and in the second quadrant. Thus, sin (t) will be positive for angles in the first and second quadrant.
