h = 2.7 (slider from 0 to 10, step 0.1)
α = 0.6457718232379019 rad (slider from 0 to 90*°, step 0.017453292519943295)
v0 = 8.3 (slider from 0 to 15, step 0.1)
f(x) = -(9.81 / (2 * v0^(2) * cos(α)^(2))) * x^(2) + tan(α) * x + h
C, D = Intersect(f, xAxis)
A = Intersect(f, yAxis)
b = Line(A, xAxis)
B, E = Intersect(f, b)
E' = Rotate(E, α, A)
β = Angle(E, A, E')
u = Vector(A, E')