Question

If the point (-5, -12) is a point on the terminal side of an angle in standard position, how do you find the radius of the circle?

Answer 1

If I got the idea of terminal side of the angle right, you could use Pitagora's Theorem to find the radius.
From the picture:

The line `AO` is the radius.
You can use Pitagora's Theorem applied to the triangle `ABO` giving:
`AO=sqrt((-5)^2+(-12)^2)=13`
Which is the radius.

Using trigonometry (in particular inverse trigonometric functions) you can also find the angle that the radius `AO` makes with the positive `x` semi-axis!