Residuals and r squared

You will list the residuals of a line, add up their squares, and work out $r^2$ as $1 - \dfrac{\text{SSE}}{S_{yy}}$. The checker uses the stopping distances of the lesson and compares $r^2$ with the square of $r$.

The idea. For each point the residual is $y - (a + bx)$. The SSE is the sum of their squares, and $S_{yy}$ is the sum of the squares of $y - \bar{y}$.

Your tasks.

1. Finish residuals(xs, ys, a, b). Return a list.
2. Finish sse(xs, ys, a, b).
3. Finish r_squared(xs, ys). Use the least-squares line from statistics.linear_regression.