There are two parts to this and I think I have figured out how to do part 1 which says: State the midpoint of the line segment with endpoints (-3,8)...

I need help figuring out what to do. There are two parts to this and I think I have figured out how to do part 1 which says:

State the midpoint of the line segment with endpoints (-3,8) and (5,10).

I found:

m = (5-3/2,10+8/2) 

m = (2/2,18/2)

m = (1, 9)

Part 2 says If the point you found in part 1 is the center of the circle, and the other two points are on the circle, find the length of the radius of the circle. I worked it out to where I found r=2√17, but I am seriously doubting myself, unsure if I have done this without error. Please help!