The unit circle is the circle with radius one centered at the origin. The equation of this circle is \(x^2+y^2=1\). If the terminal edge of an angle \(\theta\) intersects the unit circle at the point \((x,y)\), then \(\sin(\theta) = y\) and \(\cos(\theta)=x\).
Using the Applet
This applet can be used to visualize the values of the trigonometric functions at particular angles, either by seeing the equivalent points on the graphs of \(\sin(\theta)\) and \(\cos(\theta)\), or by drawing a right triangle within the unit circle. After choosing which method you'd like to see, move your mouse over the circle to change the value of the angle \(\theta\).
About this Applet