To find the radius of the circle,we would have to find the length between the point and the centre.
We can use the distance formula to find its length,here's the formula:
[tex] \sqrt{(y1 - y2)^{2} + (x1 - x2) {}^{2} } [/tex]
In this case,here's what we can do:
[tex] \sqrt{ {(3 - 1)}^{2} + {(4 - 2)}^{2} } \\ = \sqrt{4 + 4} \\ = \sqrt{8} [/tex]
Thus,the answer is _/8,which can also be written as ≈2.828(correct to 3 demical places)
Hope it helps!