Describe a method other than the one used in the example that you
could use to find a.

Answer: d ≈ 8.9 units
Step-by-step explanation:
We will use the distance formula. Let point S be the first point, and point R be the second. We will plug in the values and solve.
[tex]\displaystyle d=\sqrt{(x_{2}-x_{1})^2 +(y_{2}-y_{1})^2}[/tex]
[tex]\displaystyle d=\sqrt{3--5)^2 +(1-5)^2}[/tex]
[tex]\displaystyle d=\sqrt{(8)^2 +(-4)^2}[/tex]
[tex]\displaystyle d=\sqrt{64 +16}[/tex]
[tex]\displaystyle d=\sqrt{80}[/tex]
d ≈ 8.9 units