How to pick a method
- Substitution when you can see a function and its derivative: ∫ (log x)/x dx, put t = log x.
- By parts for a product of two different kinds of function. Choose u by ILATE: Inverse trig, Log, Algebraic, Trig, Exponential.
- Partial fractions for a ratio of polynomials, like 1/(x² − a²).
- Trig identities for powers: sin²x = (1 − cos 2x)/2, tan²x = sec²x − 1.
Log means natural log here (base e), the way NCERT and JEE write it. Add the constant C to every indefinite integral.
Questions students ask
What is the integration of 1/x?
log|x| + C.
What is ILATE?
An order for choosing u in integration by parts: Inverse trigonometric, Logarithmic, Algebraic, Trigonometric, Exponential. Pick u from whichever comes first.
What is the integration of sec x?
log|sec x + tan x| + C.
What is the integration of log x?
x log x − x + C, by parts.