Which of the Following Is an Exact Differential Equation?
$( x + y ) d x + \left( 2 y + x ^ { 2 } \right) d y$

Multiple Choice

Which of the following is an exact differential equation?

A) $( x + y ) d x + \left( 2 y + x ^ { 2 } \right) d y$
B) $( x + y ) d x + ( 2 y + x ) d y$
C) $\left( x ^ { 2 } + 2 x y \right) d x + ( 2 y + x ) d y$
D) $( x + y ) d x + \left( 2 y ^ { 2 } + 3 x y \right) d y$
E) $\left( x + y ^ { 2 } \right) d x + ( 2 y + x ) d y$