Given that the equation of circle O is the square of X + the square of y = 9, find the trajectory equation of the midpoint P of the chord of the circle through point a (1,2)?

Given that the equation of circle O is the square of X + the square of y = 9, find the trajectory equation of the midpoint P of the chord of the circle through point a (1,2)?

Because P is the point of the string
So OP is always perpendicular to pa
So the trajectory of point P is on a circle with diameter OA
The center coordinate of the circle is (1 / 2,1), and the radius is r, R & # 178; = (1 & # 178; + 2 & # 178;) / 4 = 5 / 4
So the trajectory equation of P is: (x - (1 / 2)) &# 178; + (Y-1) &# 178; = 5 / 4