The best-fit line and g in code

You will write four functions for the pendulum and the straight-line graph. They follow the least-squares formulas of the lesson.

The idea. The line $y = mx + c$ through the points has the slope $m = \dfrac{n\sum xy - \sum x\sum y}{n\sum x^2 - (\sum x)^2}$ and the intercept $c = \dfrac{\sum y - m\sum x}{n}$. For a pendulum the slope of $T^2$ against $L$ is $4\pi^2/g$.

Your tasks.

1. In slope, return the least-squares slope of the points xs, ys.
2. In intercept, return the least-squares intercept.
3. In g_from_slope, return g for the slope of the graph of $T^2$ against $L$.
4. In percent_error, return the percentage error of a result value with an absolute error delta.