a) $2\sqrt{x^{2} + 4x - 7} = \sqrt{-4x^{2} + 38x - 43}$
$\Leftrightarrow 4(x^{2} + 4x - 7) = -4x^{2} + 38x - 43$
$\Rightarrow 4x^{2} + 16x - 28 = -4x^{2} + 38x - 43$
$\Rightarrow 8x^{2} - 22x + 6 = 0$
$\Rightarrow x = \frac{3}{2}$
b) $\sqrt{6x^{2} + 7x - 1} - \sqrt{-29x^{2} - 41x + 10} = 0$
$\Leftrightarrow 6x^{2} + 7x - 1 - (-29x^{2} - 41x + 10) = 0$
$\Rightarrow 35x^{2} + 48x -11 = 0$
$\Rightarrow x = \frac{1}{5}$ và $x = -\frac{11}{7}$