Reflection of the midpoint of the line segment joining the points 1,2 and  3,4 with respect to the line y=x is a,b . The value of a+b is

Suppose that the midpoint of the line segment joining the points 1,2 and 3,4  is  PHence, P=x1+x22,y1+y22=1+32,2+42=2,3 The image of the point Px1,y1  in the line y=x is  y1,x1Therefore, the image of the point  P2,3 in the line y=x is  a,b=3,2It implies that   a+b=3+2=5