<s>[INST] $f(x - 1) + f(x − 2) $ and the sum of coeficients If $f(x-1)+f(x-2) = 5x^2 - 2x + 9$
and
$f(x)= ax^2 + bx + c$
what would be the value of $a+b+c$?
I was doing
$f(x-1)+f(x-2)= f(x-3)$
then 
$f(x)$
a = 5
b = -2
c = 9

$(5-3)+(-2-3)+(9-3)$
But do not think is is correct
What would be correct approach?
 [/INST] If $f(x) = ax^2 + bx+ c$, what is $f(x-1)$ and what is $f(x-2)$?
Work those out, then add both expressions to equate to $5x^2-2x+9$.
</s>