Equation of Circle

The coordinates of two points $A$ and $B$ are $(-1,-2)$and $(7,4)$respectively. Find the equation of the circle $C$, for which $AB$is the diameter.

The equation of a circle with centre on $y-$axis and passing through the origin and the point $(3, 4)$ is

The equation of the incircle of the triangle formed by the straight line $4x+3y=6$ with the coordinate axes is

The centre of a circle is at $\left(2, 6\right)$ and a chord of this circle of length $24$ unit is bisected at $\left(-1, 2\right)$. Find the radius of the circle.