Issues with linear and quadratic multivariate Taylor series

Hey guys

I am having a few issues with my linear algebra course. Me and my friends are in a study group and we are working on this problem for one of our seminars:

3. Find the linear and quadratic approximations to the funtion f(x,y)=e^(ax-by) around the point (0,0)

We think we have found the linear approximation of this as:

1 + xae^(ax-by) - ybe^(ax-by)

Is this correct? How do we get the quadratic approximation?

Hope you can help guys, it would be much appreciated.