A: Let m be (x, y).

Because OP=AP=4, so

Root number (x-0) 2+(y-4) 2 = root number (x 2+y 2), that is,

X^2+Y^2-8Y+ 16=X^2+Y^2

8Y= 16

Y=2

The radical number 3 of X=2

Where Y=-X+M

M=2 radical number 3+2

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If you are satisfied, I hope it can be adopted! ^_^