Trigonometric Definition with a Unit Circle.
This applet shows how sine, cosine and tangent for an angle A is defined with a unit circle. Use the slider to see to change the angle A.
Sin A is the height of the right angle triangle and is represented by the blue segment.
Cos A is the base of the right angle triangle and is represented by the red segment.
Tan A is the height of the brown segment where E is the intersection between the green ray and the tangent line at B.