If [tex]f(x) = 3 x^{2} + 5x+1[/tex] and you need to get the value of f(-1) all you need to do is substitute x with -1.
So your equation should look like this:
[tex]f(-1) = 3 (-1)^{2} + 5(-1)+1[/tex] Then we just do the operations presented
[tex]= 3(1) + (-5)+1[/tex]
[tex]= 3 +(-5) +1[/tex]
[tex]= (-2)+1[/tex]
[tex]= -1[/tex]
The value then of f(-1) = -1
