Step 1: Ensure proper fraction. If deg(P) >= deg(Q), perform polynomial long division: P/Q = quotient + remainder/Q.
Step 2: Factor the denominator Q(x). Over the reals, Q factors into products of linear factors (x-a)^k and irreducible quadratic factors (x^2+px+q)^m where p^2-4q < 0.
Step 3: Write the decomposition form.
- Linear (x-a): A/(x-a)
- Repeated linear (x-a)^k: A1/(x-a) + A2/(x-a)^2 + ... + Ak/(x-a)^k
- Quadratic (x^2+px+q): (Ax+B)/(x^2+px+q)
- Repeated quadratic: stack with increasing powers in denominator
Step 4: Find coefficients.
- Cover-up: For distinct linear factor (x-a), set x=a after removing (x-a). Quick and efficient.
- Substitution: Plug in convenient x values (usually roots of Q).
- Coefficient comparison: Match coefficients of powers of x on both sides.
Step 5: Integrate each term.
- A/(x-a) => A*ln|x-a|
- A/(x-a)^n (n>1) => A*(x-a)^(1-n)/(1-n)
- (Ax+B)/(x^2+px+q): write Ax+B = (A/2)(2x+p) + (B-Ap/2). First part gives log, second gives arctan after completing the square.
Common JEE types:
- 1/((x-a)(x-b)): two distinct linear factors
- 1/(x(x^n+1)): multiply by x^(n-1)/x^(n-1), then substitute t = x^n
- (px+q)/((x^2+a)(x^2+b)): two quadratic factors