Probeer ook [math]F(x,y) = x^2[/math], [math]F(x,y) = x^2+y^2[/math], [math]F(x,y) = x^2-y^2[/math], [math]F(x,y) = y^2-x^2[/math],[br][br][math]F(x,y) = x \cdot y[/math], [math]F(x,y) = x\cdot y^2[/math], [math]F(x,y) = x^2 \cdot y[/math], [math]F(x,y) = x^2 \cdot y^2[/math] en [math]F(x,y) =1-x-y[/math].