Limits: The Foundation of Calculus
A limit describes the value a function approaches as its input approaches some value. Limits are the rigorous foundation upon which derivatives, integrals, and continuity are defined. The notation lim(x→a) f(x) = L means f(x) gets arbitrarily close to L as x gets close to a. Limits handle cases where direct evaluation fails, such as 0/0 indeterminate forms, and they define what happens at boundaries, discontinuities, and infinity.
Methods for Evaluating Limits
1. Direct Substitution: plug in x=a
If f(a) is defined, lim = f(a)
2. Factoring: simplify 0/0 forms
(x²-1)/(x-1) = (x+1)(x-1)/(x-1) = x+1
3. L'Hôpital's Rule (0/0 or ∞/∞):
lim f/g = lim f'/g'
4. Squeeze Theorem:
If g(x)≤f(x)≤h(x) and lim g=lim h=L
then lim f = L
5. Known Limits:
lim(x→0) sin(x)/x = 1
lim(x→∞) (1+1/x)^x = e
If f(a) is defined, lim = f(a)
2. Factoring: simplify 0/0 forms
(x²-1)/(x-1) = (x+1)(x-1)/(x-1) = x+1
3. L'Hôpital's Rule (0/0 or ∞/∞):
lim f/g = lim f'/g'
4. Squeeze Theorem:
If g(x)≤f(x)≤h(x) and lim g=lim h=L
then lim f = L
5. Known Limits:
lim(x→0) sin(x)/x = 1
lim(x→∞) (1+1/x)^x = e
Indeterminate Forms
Seven indeterminate forms require special techniques: 0/0, ∞/∞, 0·∞, ∞-∞, 0⁰, ∞⁰, 1^∞. Direct substitution gives no answer for these. Use algebraic manipulation, L'Hôpital's Rule, or series expansion to resolve them.