The equation of a circle:

(h,k) - the coordinates of the centre
r - the radius
The midpoint of the diameter is the centre of a circle.
The coordinates of the midpoint:

(x₁,y₁), (x₂,y₂) - the coordinates of endpoints

The centre of the circle is (2,5).
The radius is the distance between an endpoint of the diameter and the centre.
The formula for distance:


The radius is 5.
y=1 is the answer, there is no slope, so the formula y=mx+b turns into y=b, since 1 is the intercept 1 is b.
Step-by-step explanation:
- (√3+√7)(√3+√7)
- (√3)^2+[(√3*√7)+(√3*√7)]+(√7)^2
- 3+2√21+7
- 10+2√21