# How do you find the slope of a tangent line using secant lines?

$\frac{f \left(a + h\right) - f \left(a\right)}{h}$,
then we can better approximate the slope of the tangent line by the slope of secant line by making $h$ smaller and smaller. Hence, we can find the slope of the tangent line $m$ at $x = a$ by
$m = {\lim}_{h \to 0} \frac{f \left(a + h\right) - f \left(a\right)}{h}$