A Visual Proof of the Double-Angle Formula for Sine
A Visual Proof of the Double-Angle Formula for Sine
The double-angle formula for sine states that . Computing the area of a triangle using the formula (area equals one-half base times height) gives for the top triangle and for the bottom triangle.
sin(2θ)=2sin(θ)cos(θ)
A=bh
1
2
sin(2θ)
2sin(θ)cos(θ)