Differential Equations
1. The problem asks to solve two differential equations:
a) $$\frac{dy}{dx} = \frac{1+x}{1+y}$$
b) $$\frac{dy}{dx} = \frac{x+y}{x}$$
2. Solve a) $$\frac{dy}{dx} = \frac{1+x}{1+y}$$:
Step 1: Rearrange to separate variables:
$$ (1+y) dy = (1+x) dx $$
Step 2: Integrate both sides:
$$ \int (1+y) dy = \int (1+x) dx $$
This gives:
$$ y + \frac{y^2}{2} = x + \frac{x^2}{2} + C $$
Step 3: The implicit general solution is:
$$ y + \frac{y^2}{2} = x + \frac{x^2}{2} + C $$
3. Solve b) $$\frac{dy}{dx} = \frac{x+y}{x}$$:
Step 1: Rewrite equation:
$$ \frac{dy}{dx} = 1 + \frac{y}{x} $$
Step 2: Substitute $$ v = \frac{y}{x} \Rightarrow y = vx $$
Then:
$$ \frac{dy}{dx} = v + x\frac{dv}{dx} $$
Step 3: Substitute into differential equation:
$$ v + x\frac{dv}{dx} = 1 + v $$
Simplify:
$$ x\frac{dv}{dx} = 1 $$
Step 4: Separate variables:
$$ dv = \frac{1}{x} dx $$
Step 5: Integrate both sides:
$$ \int dv = \int \frac{1}{x} dx $$
Gives:
$$ v = \ln|x| + C $$
Step 6: Recall $$ v=\frac{y}{x} $$ so:
$$ \frac{y}{x} = \ln|x| + C $$
Multiply both sides by $$ x $$:
$$ y = x\ln|x| + Cx $$
4. Final answers:
a) $$ y + \frac{y^2}{2} = x + \frac{x^2}{2} + C $$
b) $$ y = x\ln|x| + Cx $$
These solutions describe the implicit and explicit solutions to the given differential equations.