The given expression is:
[tex](6x^2+3)-(6+5x^4)[/tex]Open up the parenthesis
[tex]\begin{gathered} \text{The negative sign affects both 6 and 5x}^4 \\ \text{The expression becomes:} \\ 6x^2+3-6-5x^4 \end{gathered}[/tex]This is further simplified as:
[tex]\begin{gathered} -5x^4+6x^2-3 \\ -(5x^4-6x^2+3) \end{gathered}[/tex]