The addition of the value \ (a\) represents a vertical translation in the graph. If \ (a\) is positive, the graph translates upwards. If \ (a\) is negative, the graph translates downwards.

M. Papadimitrakis, On Convexity of Level Curves of Harmonic Functions in the Hyperbolic Plane, Proceedings of the American Mathematical Society, Vol. 114, No. 3 (Mar., 1992), pp. 695-698 ...

W. J. Walker, Boundary Behaviour of Level Curves of Harmonic Functions, Proceedings of the American Mathematical Society, Vol. 91, No. 1 (May, 1984), pp. 102-104 ...

The area under a curve can be estimated by dividing it into triangles, rectangles and trapeziums. If we have a speed-time or velocity-time graph, the distance travelled can be estimated by finding ...