If C (2,3) is the centre of circle and A (1,-2) is one end of the diameter AB, find the coordinate of B.

(3,8) because if you find the change in values, A is - 1 in the x value, and - 5 in the y value. So if you make them posistive because you are going the opposite direction, you add them to C and get (2+1=3,3+5=8) or (3,8)