$${ x }^{ m+1 } - { x }^{ n-2 } + { x }^{ m } { x }^{ n-1 }$$
$x^{m+n-1}+x^{m+1}-x^{n-2}$
$\left(m+n-1\right)x^{m+n-2}-\left(n-2\right)x^{n-3}+\left(m+1\right)x^{m}$
