$\textcolor{3333CC}{f(x,y)=}$

f(x, y) = sin(x) + y / 12
f'_{y} = Derivative(f, y)
P = PointIn(xOyPlane)
f'_{x} = Derivative(f, x)
F: P + (0, 0, f(P))
delta_{x}: {{x - x(P)}, {y - y(P)}}
nabla_{f}: {{f'_{x}(P), f'_{y}(P)}}
Eingabefeld1 = Textfield(f)
gradText: "\text{grad }f = (" + (LaTeX[f'_{x}]) + " , " + (LaTeX[f'_{y}]) + ")"
a = Simplify(Element[f(P) + (nabla_{f} * delta_{x}), 1, 1])
T(x, y) = If[x(P) - 2 ≤ x ≤ x(P) + 2 ∧ y(P) - 2 ≤ y ≤ y(P) + 2, a(x, y)]
g = Segment(P, F)