# Evaluating Polynomial Function

#### evking

##### New member
The question is f(x[SUP]2[/SUP])=-x[SUP]2[/SUP]+5x-2 So I plugged in the X[SUP]2[/SUP] as X and got -x[SUP]4[/SUP]+5x[SUP]2[/SUP]-2 but the multiple choice only has -4[SUP]​4[/SUP]+x[SUP]2[/SUP]-2, and if the multiple choice is correct what happened to the 5?

Last edited:

#### Bob Brown MSEE

##### Full Member
What's the question?

The question is f(x[SUP]2[/SUP])=-x[SUP]2[/SUP]+5x-2 So I plugged in the X[SUP]2[/SUP] as X and got -x[SUP]4[/SUP]+5x[SUP]2[/SUP]-2 but the multiple choice only has -4[SUP]​4[/SUP]+x[SUP]2[/SUP]-2, and if the multiple choice is correct what happened to the 5?
It helps us if you give us the problem exactly as it was written when you got it.

Was the question, "What is f(x)?" ?
Was one choice, "-x + 5Sqrt[x] -2" ?

#### evking

##### New member
It helps us if you give us the problem exactly as it was written when you got it.

Was the question, "What is f(x)?" ?
Was one choice, "-x + 5Sqrt[x] -2" ?
The question says " Polynomial Functions are shown below, plug in the following values as X to get the output values."
I know for sure that -x[SUP]4[/SUP]+x[SUP]2[/SUP]-2 is the answer that is considered correct for that problem because it was graded as correct I am just curious why it is considered correct instead of -x[SUP]4[/SUP]+5x[SUP]​2[/SUP]-2. Hope that helps.

#### Ishuda

##### Elite Member
The question says " Polynomial Functions are shown below, plug in the following values as X to get the output values."
I know for sure that -x[SUP]4[/SUP]+x[SUP]2[/SUP]-2 is the answer that is considered correct for that problem because it was graded as correct I am just curious why it is considered correct instead of -x[SUP]4[/SUP]+5x[SUP]​2[/SUP]-2. Hope that helps.

As a spin off from Bob Brown's post:
Two things:
(1) Is the original polynomial
f(x) = -x[SUP]2[/SUP]+5x-2
so that, in reality,
f(x[SUP]2[/SUP]) = -x[SUP]4[/SUP]+5x[SUP]2[/SUP]-2

(2) If that is the original polynomial 'printed in the book' it looks like maybe a typo and it should have been
f(x) = -x[SUP]2[/SUP]+x-2
so that
f(x[SUP]2[/SUP]) = -x[SUP]4[/SUP]+x[SUP]2[/SUP]-2