Determine If Is Everywhere Continuous, and If Not, Locate the Point(s) of \begin{array}

Essay

Determine if $f ( x , y ) = \left\{ \begin{array} { l l } \frac { x ^ { 2 } + x y } { x ^ { 2 } + y ^ { 2 } } & \text { if } ( x , y ) \neq ( 0,0 ) \\1 & \text { if } ( x , y ) = ( 0,0 )\end{array} \right.$ is everywhere continuous, and if not, locate the point(s) of discontinuity.