Note that the notation [tex](f+g)(x)[/tex] is just another way of writing [tex]f(x)+g(x)[/tex]. Here, we're simply taking the expression for f(x) and adding the expression for g(x) to it. Together, we have:
[tex]f(x)=2x-5\\g(x)=x^2-4x-8[/tex]
Which means that
[tex](f+g)(x)=f(x)+g(x)=(2x-5)+(x^2-4x-8)[/tex]
And from there, it's just a matter of combining like terms to simplify.
