Find the Linear Approximation to the Function $f ( x , y ) = 2 x ^ { 2 } + y ^ { 2 }$

Essay

Find the linear approximation to the function $f ( x , y ) = 2 x ^ { 2 } + y ^ { 2 }$ at $( 1,1 )$ and use it to approximate $f ( 1.1,1.1 )$ .