Evalute the function at the given value of the independent variable and simplify.

f(x)=2x^2-5x+6; f(x-1)- I got 2x^2-9x+13

I still keep on getting the same answer.

f(x-1) = 2(x-1)^2 -5(x-1) +6

= 2x^2 -4x +2 -5x +5 +6
= 2x^2 -9x +13

I agree with your answer