Equivalencias asintóticas (infinitésimos)

Casos continuos: función de x, con u→0

sinuu\sin u \sim usin(3x)3x\sin(3x) \sim 3x
tanuu\tan u \sim utan(x2)x2\tan(x^{2}) \sim x^{2}
arcsinuu\arcsin u \sim uarcsin(2x)2x\arcsin(2x) \sim 2x
arctanuu\arctan u \sim uarctan ⁣(x2)x2\arctan\!\left(\tfrac{x}{2}\right) \sim \tfrac{x}{2}
sinhuu\sinh u \sim usinh(4x)4x\sinh(4x) \sim 4x
1cosuu221-\cos u \sim \dfrac{u^{2}}{2}1cos(2x)2x21-\cos(2x) \sim 2x^{2}
eu1ue^{u}-1 \sim ue3x13xe^{3x}-1 \sim 3x
au1ulna(a>0)a^{u}-1 \sim u\ln a \quad(a>0)2x1xln22^{x}-1 \sim x\ln 2
ln(1+u)u\ln(1+u) \sim uln(1+5x)5x\ln(1+5x) \sim 5x
(1+u)r1ru(r0)(1+u)^{r}-1 \sim r\,u \quad(r\neq0)1+x1x2\sqrt{1+x}-1 \sim \tfrac{x}{2}

Casos discretos: sucesión aₙ, con n→∞

sin ⁣(1n)1n\sin\!\left(\tfrac1n\right) \sim \tfrac1nnsin ⁣(1n)1n\sin\!\left(\tfrac1n\right) \to 1
ln ⁣(1+1n)1n\ln\!\left(1+\tfrac1n\right) \sim \tfrac1nnln ⁣(1+1n)1n\ln\!\left(1+\tfrac1n\right) \to 1
e1/n11ne^{1/n}-1 \sim \tfrac1nn(e1/n1)1n\left(e^{1/n}-1\right) \to 1
aknk++a0aknk(ak0)a_k n^{k} + \dots + a_0 \sim a_k n^{k} \quad(a_k\neq0)3n2+n2n2532\dfrac{3n^{2}+n}{2n^{2}-5} \to \tfrac32
n!2πn(ne)n  (Stirling)n! \sim \sqrt{2\pi n}\left(\dfrac{n}{e}\right)^{n}\ \ \text{(Stirling)}n!nn0\dfrac{n!}{n^{n}} \to 0