Problem 123
Find the general integral of 2x(1+√(x^2-y))dx-√(x^2-y) dy=0
Find the general integral of $2x\left(1+\sqrt{x^2-y}\right)dx-\sqrt{x^2-y}\,dy=0$.
Explanation of Method
The radical suggests the substitution $u=x^2-y$, which eliminates $x$ and $y$ separately in favor of $u$ and $x$, reducing the equation to a separable one.
Step 1: Substitute $u=x^2-y$
Then $dy=2x\,dx-du$. Substituting: $2x(1+\sqrt{u})\,dx-\sqrt{u}(2x\,dx-du)=0$, and the $2x\sqrt{u}\,dx$ terms cancel, leaving
\[2x\,dx+\sqrt{u}\,du=0.\]
Step 2: Integrate
$x^2+\dfrac23u^{3/2}=C_1$. Multiplying by $\tfrac32$ and relabeling the constant:
Step 3: Back-substitute
With $u=x^2-y$:
Result
Final answer:
\[\boxed{\,(x^2-y)^{3/2}+\frac32x^2=C,\qquad C\in\mathbb{R}}\]