# Limits: Power Function, can't get same answer!

1. Oct 6, 2008

### CougarXLS

1. The problem statement, all variables and given/known data:

The question asks to find the limit as x approaches 8 of (2x^2 - 3x + 4).
So I use the limit law/property which states that if f is a polynomial or rational function and if a is in the domain of f, then the limit of f(x) as x approaches a is f(a). Correct?

2. Relevant equations:

Now, since the limit law I described clearly fits as this is a polynomial expression, and x can be any real number, I plug in 8, aka f(a) = f(8). The answer I get does not agree with the answer key.

3. The attempt at a solution:

Calculus never came easy for me, but here is my attempt:
lim x->8 (2x^2 - 3x + 4)
= 2(8)^2 - 3(8) + 4
= 108
Do I even have the right approach??
lim x->8 (2x^2 - 3x + 4)
= 2(5)^2 - 3(5) + 4
= 39

Assuming no error in the actual substitutions & calculation, where the heck did the key get 5??? Am I missing something here, or is the answer key throwing out a red herring? 99.99% of the time, whenever the answer key disagrees with my answer: I did something wrong.
What happened this time? It seems like that instead of using 8, they used 5... why?

2. Oct 6, 2008

your work with $$8$$ is correct.

One of two possiilities:
1) The question was written with 8 when it should have been 5
2) The answer was written with 5 when it should have been 8
:uhh:

A minor chance - you are looking at the wrong solution, but since the polynomial matches the chance of that seems very low.

3. Oct 7, 2008