$\dfrac{24}{x + 4} + \dfrac{24}{x - 4} = 2,5$
ĐKXĐ: $x \neq \pm 4$
Quy đồng- khử mẫu ta được:
$24(x - 4) + 24(x + 4) = 2,5(x - 4)(x + 4)$
$\Leftrightarrow 24x - 96 + 24x + 96 = 2,5x^2 - 40$
$\Leftrightarrow 2,5x^2 - 48x - 40 = 0$
$\Leftrightarrow x^2 - 19,2x - 16 = 0$
$\Delta = 19,2^2 + 4.1.16 = 402,64$
$\sqrt{\Delta} = \sqrt{402,64} = 20,8$
$x_1 = \dfrac{19,2 - 20,8}{2} = - 0,8$
$x_2 = \dfrac{19,2 + 20,8}{2} = 20$
