Svaret er det grønne v.

a1 = 0.5 (slider from -5 to 5, step 0.1)
b1 = 0.8 (slider from -5 to 5, step 0.1)
a: y = (a1 * x) + b1
a2 = -0.8 (slider from -5 to 5, step 0.1)
b2 = -0.7 (slider from -5 to 5, step 0.1)
b: y = (a2 * x) + b2
A = Intersect(a, b)
c: y = y(A)
v1: atan(a1)
v2: atan(a2)
v: abs(v1 - v2)
α = Angle(b, a)
β = Angle(a, b)
γ: α + β