$\sin x \underset{x\to0}= x - \frac{x^3}{3!} + \frac{x^5}{5!} - o(x^5)$
$\cos x \underset{x\to0}= 1 - \frac{x^2}{2!} + \frac{x^4}{4!} - o(x^4)$
$e^x \underset{x\to0}= 1 + x + \frac{x^2}{2!} + \frac{x^3}{3!} + o(x^3)$
$(1+x)^p \underset{x\to0}= 1 + px + \frac{(p-1)px^2}{2!} + \frac{(p-2)(p-1)x^3}{3!} + o(x^3)$
$f(x) \underset{x\to x_0}= f(x_0) + f'(x_0)(x-x_0) + \frac{f''(x_0)(x-x_0)^2}{2!} + \dots$
$e^{i\phi} = \cos(\phi)+i\cdot\sin(\phi)$
$e^{ix} = 1+ix-\frac{x^2}{2!} - i*\frac{x^3}{3!} +\frac{x^4}{4!} + i*\frac{x^5}{5!}+ o(x^5)$
$\ln(1 + x) \underset{x\to0}= x -\frac{x^2}2+\frac{x^3}3-\frac{x^4}4+o(x^4)$
$\arctg(x) \underset{x\to0}= x-\frac{x^3}3+\frac{x^5}5-\frac{x^7}7+o(x^7)$
$\mathbb N \sub \mathbb Z \sub \mathbb Q \sub \mathbb R$
Опишем $\mathbb N$: