Show That the Surface Areas for the Functions $f ( x , y ) = 2 x ^ { 2 } + 2 y ^ { 2 }$

Essay

Show that the surface areas for the functions $f ( x , y ) = 2 x ^ { 2 } + 2 y ^ { 2 }$ and $g ( x , y ) = 4 x y$ over the disk $D = \left\{ ( x , y ) \mid x ^ { 2 } + y ^ { 2 } \leq 1 \right\}$ are equal.