## Precalculus (6th Edition)

The results in Exercises 86 and 87 are $\sqrt{10}$ and $2\sqrt{10}$, respectively. Thus, their sum is: sum $=\sqrt{10} + 3\sqrt{10} = 3\sqrt{10}$ The result in Exercise 89 is $3\sqrt{10}$. Therefore, the distance from the 1st point to the 4th point is equal to the sum of the distance between the first two points and the distance between the 2nd and the 4th point.