Finally, the company also wishes to know how well certain data fit the polynomial behavior expected. (maybe there's something else going on from the theoretical models they're using.) therefore they have asked you to provide a function which calculates the so-called r^2 value, an assessment of how well a model fits data points. compose a function r_sqr which accepts an array of polynomial coefficients and an array of data points and returns the r^2 value for the model and data set.