Let L 1 and L 2 denote two nonvertical intersecting lines, and let denote the acute angle between L 1 and L 2 (see

Let L₁ and L₂ denote two nonvertical intersecting lines, and let θ denote the acute angle between L₁ and L₂ (see the figure). Show that 

where m₁ and m₂ are the slopes of L₁ and L₂, respectively.

Use the facts that tan θ₁ = m₁ and tan θ₂ m₂.

L2 02