1. The problem statement, all variables and given/known data 1. (a) Find the equation of the circle with the straight line joining A(1;-1) and C(3; 4) as diameter. (b) Hence or otherwise, derive the general formula (x - x1)(x - x2) + (y - y1)(y - y2)=0 of the equation of a circle for the points A(x1; y1) and C(x2; y2): 2. Relevant equations 3. The attempt at a solution I did part a) but part b) is baffling me could someone give me a hint on what to do?