
Doug C. answered 04/18/20
Math Tutor with Reputation to make difficult concepts understandable
In the 2nd quadrant sinx is positive and cosx is negatvie, so rule out 2nd quadrant ahgles.
IN the 1st quadrant ask yourself where does sinx = cosx,? Only at pi/4. On the unit circle visualize angles starting at 0 and moving towards pi/4. At 0, sinx = 0 and cosx = 1. At pi/6 (for example), the y coordinate (sin x) the point on the unit circle is .5, but x coordinate is √3/2 (0.866). As the angle moves past pi/4, the y coordinates become greater then the x-coordinates.