Write Using Negative Exponents x^4+3x

$x^{4} + 3 x$

Move $x^{4}$ in $\frac{x^{4}}{1}$ to the denominator and change the exponent from positive to negative.

$\frac{1}{x^{- 4}}$

Move $x^{1}$ in $\frac{3 x}{1}$ to the denominator and change the exponent from positive to negative.

$\frac{3}{x^{- 1}}$

Rewrite the expression with the negative exponents.

$\frac{1}{x^{- 4}} + \frac{3}{x^{- 1}}$