Partial Derivatives & the Gradient · Hard problem

Let $f(x,y) = e^{x}\cos y$. The linear approximation at $(0,0)$ estimates $f(0.2,0.1)$ with some error. Using the quadratic (second-order) Taylor correction term, find the SIZE of that correction (i.e. $\tfrac12\big(f_{xx}\,dx^2+2f_{xy}\,dx\,dy+f_{yy}\,dy^2\big)$ at $dx=0.2,\ dy=0.1$). Give an exact answer as a decimal.