If a,b,c  are in arithmetic progression, then 1a+b,1a+c,1b+c  are in

1a+b,1a+c,1b+c  are in AP, if        1a+c-1a+b=1b+c−1a+cie,  if    b−ca+b=a−bb+cie,  if      b−a=a−b,  which is true.