f(x) = x⁴ - 3 x² - x + 1
A = Point(f)
B = Point(f)
a = Segment(A, B)
b = OrthogonalLine(A, xAxis)
c = OrthogonalLine(B, xAxis)
d = OrthogonalLine(B, b)
C = Intersect(b, d)
T2: "\Delta x=" + (x(B) - x(A))
T3: "\frac{\Delta f}{\Delta x}=" + ((y(B) - y(A)) / (x(B) - x(A)))
T1: "\Delta f=" + (y(B) - y(A))
e = Tangent(A, f)