Part of CALC-07 — Differential Equations

JEE Previous Year DE Patterns

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Pattern 1: Linear DE with IF (Most Frequent) JEE gives dy/dx + P(x)y = Q(x) with a specific IF. Common IFs: xnx^n, sec x, e^(x2x^2), (1+x2x^2). The solution form yIF = integral QIF dx + C is applied with an initial condition to find C.

Pattern 2: Homogeneous DE (High Frequency) Given dy/dx = ax+by(cx+dy)\frac{ax+by}{(cx+dy)}, recognize homogeneity and use y = vx. JEE often asks for the curve passing through a specific point.

Pattern 3: Formation of DE (Moderate) Given a 1- or 2-parameter family, find the DE. Key: count constants to determine order, then differentiate and eliminate.

Pattern 4: Bernoulli Equation (Moderate) dy/dx + Py = QynQy^n typically with n=2 or n=-1. Recognize the yny^n term on the right side.

Pattern 5: Exact Differentials (Moderate) Recognizing d(xy), dyx\frac{y}{x}, d(arctanyx\frac{y}{x}) in disguised forms. JEE loves x dy - y dx expressions.

Pattern 6: Application Problems (Moderate) Growth/decay, cooling, or geometric properties (subnormal, subtangent). These translate to standard DE types.

Time-saving tips:

  • Check separable first (quickest)
  • For dy/dx = linearinx,y(linearinx,y)\frac{linear in x,y}{(linear in x,y)}: check homogeneity, then try linear
  • If yny^n appears on RHS, it's Bernoulli
  • x dy + y dx or x dy - y dx signals exact differential
  • Always verify by substituting back if time permits

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