The regression line: ^
y =3+2x has been fitted to the data points (4,8),(2,5) and (1,2). The residual sum of squares will be?
The formula (which you should already know or have been able to look up) is here: Residual sum of squares - Wikipedia, the free encyclopedia
Your question is mere arithmetic computation. Where are you stuck?
The residuals are the difference between your true y's...8,5,2 and the fitted y's. To get the fitted y's you estimate y via your line.
So plug in x=4,2,1 to get the fitted values of y.
Take the difference and that's your residuals.
Square and add (and shake not stir) and you have SSE, sums of square due to error/residual.