The data file: https://docs.google.com/spreadsheets/d/1YlFRTFJ1E0W6yRlvWtld-EQJNKw4SV7k4zbLVW89NDY/edit?usp=sharing

contains observations on 500 single-family houses SOLD DURING 2019/20. The data include sale price (in thousands of dollars), PRICE, and total interior area of the house in hundreds of square feet, SQFT.

a) Estimate the quadratic regression model PRICE = a1 + a2SQFT2 + e.

b) Graph the fitted curve for the model in part (c). On the graph, sketch the line that is tangent to the curve for a 2000-square-foot house.

For the regressions in (b) and (c), compute the least squares residuals and plot them against SQFT. Do any assumptions appear violated?