Question

Find the upper boundfor the magnitude |E| of the error in the approximation f(x,y)~L(x,y) over the rectangle R. F(x,y)=x^2-3XY+5 at P(2,1) R:|x-2|<=.1 |y-1|<=.1

Linearization L(x,y) is x-6y+7, which is correct, but I do not understand how to compute the error (answer is .06).