Đáp án:
$\dfrac{\Delta y}{\Delta x}=\dfrac{-1}{x(x+\Delta x)}$
Giải thích các bước giải:
Ta có: $\Delta y=-f(x)+f(x+\Delta x)$
$\to \Delta y=-\dfrac 1x+\dfrac 1{\Delta x+x}$
$\to \Delta y=\dfrac{x-x-\Delta x}{x(x+\Delta x)}$
$\to \Delta y=\dfrac{-\Delta x}{x(x+\Delta x)}$
$\to \dfrac{\Delta y}{\Delta x}=\dfrac{-1}{x(x+\Delta x)}$