$ f_k(x)\,=\,kx\cdot e^{-x^2} $

k = 4.3 (slider from -10 to 10, step 0.1)
f(x) = k * x * ℯ^(-x^(2))
A = Point(f)
a = Tangent(A, f)
B = Intersect(a, xAxis)