Ep=Em

Curseur X

Ep(x) = (-cos(x))
Em = 1.35 (slider from -5 to 5, step 0.05)
v_+(x) = sqrt(Em - Ep(x))
v_-(x) = (-sqrt(Em - Ep(x)))
D: y = Em
Curseur = -7.1 (slider from -10 to 10, step 0.01)
A: (Curseur, Ep(Curseur))
a = Line((Curseur, 0), A)