$3x+4$3x+4

$\displaystyle \frac{3x-4}{3x+4}$\displaystyle \frac{3x-4}{3x+4}

$3x-4$3x-4

$\displaystyle \frac{3x+4}{3x-4}$\displaystyle \frac{3x+4}{3x-4}