Question

Решить предел : lim = ((3*x+5)(ln(x+5)-ln(x)) x->+oo

Answer 1

$\lim_{n \to \infty} (3x+5)(ln(x+5)-lnx) = \lim_{n \to \infty} (3x+5)ln \frac{x+5}{x} = \\ \\ = \lim_{n \to \infty} ln (\frac{x+5}{x} )^{3x+5}= \lim_{n \to \infty} ln (1+\frac{5}{x} )^{3x+5}= \\ \\ = ln (\lim_{n \to \infty} (1+\frac{5}{x} )^{3x+5}) = ln (\lim_{n \to \infty} (1+\frac{5}{x} )^{ \frac{x}{5} \frac{5}{x} (3x+5)}) = \\ \\ = ln ((\lim_{n \to \infty} (1+\frac{5}{x} )^ \frac{x}{5} )^{ 15+ \frac{5}{x} }) =$

$= ln ((\lim_{n \to \infty} (1+\frac{5}{x} )^ \frac{x}{5} )^{ \lim_{n \to \infty}(15+ \frac{5}{x}) }) = ln e^{ \lim_{n \to \infty}(15+ \frac{5}{x}) } = \\ \\ = \lim_{n \to \infty}(15+ \frac{5}{x}) = 15$