Simplest Interpolating Polynomial

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Homework Statement


Consider the data in the following table for constant-pressure specific heat, C
p (kJ/kg.K) at various temperatures T (K). Determine the simplest interpolating polynomial that is likely to predict Cp within 1% error over the specified range of temperature.

T : 1000 1100 1200 1300 1400 1500
Cp 1.410 1.1573 1.1722 1.1858 1.1982 1.2095




Homework Equations





The Attempt at a Solution


I am very confused, i am studying ''general least squares,polynomial regression, linear regression, Newton's interpolating polynomials, lagrange interpolating polynomials'' now. I have a question but i don't know which method i should use, can you help me quickly? Thanks. This is my question:
 
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Since the problem says "interpolating polynomials", that let's out any least squares or regression- and, here, both Newton's and Lagrange's methods should give the same fifth degree polynomial.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...

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