Question
( frac{d y}{d x}=frac{1+y^{2}}{1+x^{2}} )
( Rightarrow int frac{d y}{1+y^{2}}=int frac{d x}{x^{2}+1}+c )
( Rightarrowleft[tan ^{-1} y=tan ^{-1} x+cright. )

Solve the equation (1+x²)dy-(1+y?) dx = 0 E (1+x²)dy--(1+ y²) dx = 0
Solution
