Hello from MrBillDoesMath!
Answer: 2
Description. Create a line from point A perpendicular to the x axis. This line, with the radius (OA) , and x axis, form a right triangle. By Pythagoras,
x-length y-length hypotenuse squared
( 3 ^ (1/2) ) ^ 2 + 1 ^ 2 = 3 + 1 = 4
So, the square of the hypotenuse (or radius OA in this case) is 4. That means OA is the square root of 4 or 2.
Regards, MrB