If 1bāa+1bāc=1a+1c, then a,b,c, are in
H.P
1b−a+1b−c=1a+1c
2b−a−c(b−a)(b−c)=a+cac
2abc−a2c−ac2=(b2−ab−bc+ac)(a+c)
2abc−a2c−ac2=b2a−a2b−abc+a2c+cb2−abc−bc2+ac2
∴ 4abc−2a2c−2ac2−b2a+a2b−cb2+bc2=0
⇒(2b−1a−1c)=0
2b=1a+1c answer H.P