On the "Rate Your Professor.com website, you can rate your professors "Easiness" and "Quality" on a scale of 1-5, with higher numbers signifying easier (or higher quality) professors. At right is a scatterplot containing the ratings of all the math professors at SPSCC who had been rated at least 20 times as of Spring 2016, when I collected this data. The black dot, for example, is me. (My average E&Q scores were 2.6 and 3.3 respectively.) The line running through the data is called a "least-squares line" (also called a "regression line" or "best-fit line"). No doubt you've seen such

MATLAB: An Introduction with Applications
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On the "Rate Your Professor.com" website, you can rate your professors’ “Easiness” and “Quality” on a scale of 1-5, with higher numbers signifying easier (or higher quality) professors. At right is a scatterplot containing the ratings of all the math professors at SPSCC who had been rated at least 20 times as of Spring 2016, when I collected this data. The black dot, for example, is me. (My average E&Q scores were 2.6 and 3.3 respectively.)

The line running through the data is called a “least-squares line” (also called a “regression line” or “best-fit line”). No doubt you’ve seen such lines before. But where do they come from? The slope and y-intercept of such a line are precisely determined by the coordinates of the various data points. In this extra credit problem, you’ll learn how.

Suppose we have \( n \) pairs of data: \( (x_1, y_1), (x_2, y_2), \ldots, (x_n, y_n) \).
The line we seek will ultimately have the form \( y = mx + b \). Our task is to determine the numerical values of \( m \) and \( b \).

When we consider any specific line as a candidate for the “best fit,” we judge its quality as follows: The vertical distances between the data points and the line are called residuals. The “best-fit” line is the one that minimizes the sum of the squared residuals. (Hence the name “least-squares” line.) In other words, we want to choose \( m \) and \( b \) so that they will minimize the function

\[
S(m, b) = \sum_{i=1}^{n} (mx_i + b - y_i)^2.
\]

### Your problems (You’ll need to write up your work on the blank pages that follow):

**EC1.** Prove that \( m \) and \( b \) can be found by solving this system of linear equations:

\[
m \sum x_i^2 + b \sum x_i = \sum x_i y_i \quad \text{and} \quad m \sum x_i + nb = \sum y_i,
\]

where the sums all run from \( i = 1 \
Transcribed Image Text:On the "Rate Your Professor.com" website, you can rate your professors’ “Easiness” and “Quality” on a scale of 1-5, with higher numbers signifying easier (or higher quality) professors. At right is a scatterplot containing the ratings of all the math professors at SPSCC who had been rated at least 20 times as of Spring 2016, when I collected this data. The black dot, for example, is me. (My average E&Q scores were 2.6 and 3.3 respectively.) The line running through the data is called a “least-squares line” (also called a “regression line” or “best-fit line”). No doubt you’ve seen such lines before. But where do they come from? The slope and y-intercept of such a line are precisely determined by the coordinates of the various data points. In this extra credit problem, you’ll learn how. Suppose we have \( n \) pairs of data: \( (x_1, y_1), (x_2, y_2), \ldots, (x_n, y_n) \). The line we seek will ultimately have the form \( y = mx + b \). Our task is to determine the numerical values of \( m \) and \( b \). When we consider any specific line as a candidate for the “best fit,” we judge its quality as follows: The vertical distances between the data points and the line are called residuals. The “best-fit” line is the one that minimizes the sum of the squared residuals. (Hence the name “least-squares” line.) In other words, we want to choose \( m \) and \( b \) so that they will minimize the function \[ S(m, b) = \sum_{i=1}^{n} (mx_i + b - y_i)^2. \] ### Your problems (You’ll need to write up your work on the blank pages that follow): **EC1.** Prove that \( m \) and \( b \) can be found by solving this system of linear equations: \[ m \sum x_i^2 + b \sum x_i = \sum x_i y_i \quad \text{and} \quad m \sum x_i + nb = \sum y_i, \] where the sums all run from \( i = 1 \
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