This demo shows the linear function in two variables L(x,y) = px + qy +k over the rectangular domain 0 ≤ x ≤ 1, 0 ≤ y ≤ 1. You can change the constants p,q and k using the respective red, blue or purple slide bar, and the Graph: L(x,y) window will show the function graph of L(x,y) with the chosen values for the constants.

If you slide the hotspot on the purple slidebar, (thereby varying the constant k) the function graph is translated up and down in the directon of f(x,y). Varying p,and r on the red and blue slidebars will scale in the x- and y- direction of the graph.