$a.$ Find the linear approximation for the following function $at$ the given point.

$b.$ Use part $(a)to$ estimate the given function value.

$f(x,y)=-4x^2+4y^2$;$(5,-3)$; estimate $f(5\mathrm{.}1,-2\mathrm{.}97)$

$a.L(x,y)=$

$b.L(5\mathrm{.}1,-2\mathrm{.}97)=(Typean$ integer $or$ a decimal.$)$