Respuesta :

Solution

For this case we have this function given:

[tex]f(x)=5x+3x^2[/tex]

And we want to find -f(x) so we can do this:

[tex]-f(x)=-5x-3x^2[/tex]

And we can take common factor x and we got:

[tex]-f(x)=-x(5+3x)[/tex]