Answer
-4x$^5$-9x$^3$+8
Work Step by Step
Distribute the negative sign to the parentheses and then combine like terms vertically.
$\quad3x^5-5x^3+6$
$\underline{-(7x^5+4x^3-2)}$
$\qquad\quad\downarrow$
$\quad3x^5-5x^3+6$
$\underline{\;-7x^5-4x^3+2}$
$\;-4x^5-9x^3+8$
