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GeoGebraGeoGebra Classroom

Sine and Cosine of Two Angles

A construction show cos(A+B) = cos(A)cos(B) - sin(A)sin(B) sin(A+B) = sin(A)cos(B) + cos(A)sin(B) All lengths are measured relative to a unit of AC. The c's and s's are short forms for cos() and sin(). The blue triangles are similar. Move points A, C and W to show different geometrical arrangements.