1. Definition of Continuity
A function f(x) is continuous at a point x = a if and only if:
lim (x→a⁻) f(x) = lim (x→a⁺) f(x) = f(a)
Concept: For a function to be continuous, it must be defined at the point, and the limit as it approaches that point from both sides must equal the function's value.