Question

Доказательство с применением производной. Помогите()

Answer 1

$f(x) = \frac6x\\f(x + \Delta x) = \frac{6}{x+\Delta x}\\\Delta y = f(x + \Delta x) - f(x) = \frac{6}{x+ \Delta x} - \frac6x = \frac{6x - 6x - 6\Delta x}{x(x + \Delta x)} = \frac{-6\Delta x}{x(x + \Delta x)}\\\\\frac{\Delta y}{\Delta x} = \frac{-6}{x^2 + \Delta x \cdot x}\\\\\lim\limits_{\Delta x\to0}\frac{\Delta y}{\Delta x} = \lim\limits_{\Delta x\to0}\frac{-6}{x^2 + \underbrace{\Delta x\cdot x}_{\to0}} = -\frac{6}{x^2}$