[b]Instructions[br][/b]Push the slider for theta back to 0. Then press the Play button. Thereafter, you will see the curve [i]y[/i] = sin [i]x[/i] being traced out as the angle theta increases.[br][br][b]How this applet works[br][/b]The circle is a unit circle i.e., it has radius of 1, and it is centred at the origin [i]O[/i]. A right-angled triangle is produced (as theta changes) such that the hypotenuse is always the radius of the circle, which is 1 unit long, and [i]y[/i] is the opposite side. Thus. sin theta = [i]y[/i]/1 = [i]y[/i], so the y value of triangle will always be equal to the corresponding [i]y-[/i]value on the sine curve.