b = 2 (slider from 2 to 3, step 1.0E-4)
f(x) = b^(x)
f'(x) = f'(x)
A = Intersect(f, yAxis, (0, 1))
a = Slope(Tangent[A, f])
B = Intersect(f', yAxis, (0, 0.6931471805599453))
e = Tangent(B, f)