The most tested type in JEE. Standard form: dy/dx + P(x)*y = Q(x). Step 1: Identify P(x) and Q(x). Step 2: Compute IF = e^(integral of P(x) dx). Step 3: Multiply the entire equation by IF. Step 4: The left side becomes d/dx[y * IF]. Step 5: Integrate: y * IF = integral of Q(x) * IF dx + C. Common IFs: for P = 1/x, IF = x; for P = -1/x, IF = 1/x; for P = 2x, IF = e^($x^2$); for P = tan(x), IF = sec(x); for P = -cot(x), IF = sin(x). The key insight is that multiplying by IF makes the left side an exact derivative. If the equation is naturally dx/dy + P(y)*x = Q(y), treat x as the dependent variable.