05 Complete curve sketching
Draw y = f(x) by collecting the information in this order:
- Domain and any values excluded (denominators, even roots, logarithms).
- Intercepts: set x = 0 for the y-intercept and solve f(x) = 0 for the x-intercepts.
- Symmetry: even function → symmetric about the y-axis; odd → symmetric about the origin.
- Asymptotes: vertical where the denominator vanishes, horizontal from the limit as x → ±∞ (compare degrees).
- Stationary points with their nature, from f′ and f″.
- Points of inflection and the concavity on each side.
- End behaviour: the sign of the leading term as x → ±∞, then join the points smoothly.
Example: y = x³ − 3x. Odd function; intercepts at x = 0, ±√3; y′ = 3x² − 3 ⟹ max (−1, 2), min (1, −2); y″ = 6x ⟹ inflection (0, 0); as x → ∞, y → ∞.