Similar to the parametric question I recently posted, I need to find a value of c such that a piecewise multivariate function is continuous over an interval, not too sure where to start, because c is not only in the functon, but in the range.

Not too sure where to start here, any pointers in the right direction?Find all values of c, such that

$\displaystyle f(x,y) =\left\{\begin{array}{cc}\frac{x}{y+c},&\mbox{ if }

x \in R, y \geq 1-c\\xy, & \mbox{ if } x \in R, y< 1-c\end{array}\right. $

is continuous on $\displaystyle R^2$.