Write the equation of the circle that satisfies each set of conditions.

1.The endpoints of the diameters are (5,6) and (2,3)?

2. The circle passes through origin and has its center at (-4,3).

Now I know the standard form of the equation of a circle is

(x-h)^2+(y-k)^2=r^2

But how would I solve these two problems I mean for number 2 I know x and y but no the radius.