Simplify (9x^3)/(5x+1)-(8x^3)/(5x+1)

$\frac{9 x^{3}}{5 x + 1} - \frac{8 x^{3}}{5 x + 1}$

Combine the numerators over the common denominator.

$\frac{9 x^{3} - 8 x^{3}}{5 x + 1}$