Not who you responded to, but as he stated, the best method is the unit circle. Take a circle of radius 1 around the origin. Draw a line with angle x through t

Not who you responded to, but as he stated, the best method is the unit circle. Take a circle of radius 1 around the origin. Draw a line with angle x through the origin. The point where this line intersects the circle has vertical position sin x and horizontal position cos x. Moreover, if you measure the angle in radians, x is how much of the unit circle your angle covers. This also immediately makes the identity (sin x)^2 + (cos x)^2 = 1 obvious. https://en.wikipedia.org/wiki/Unit_circle https://en.wikipedia.org/wiki/Unit_circle