If a,b,c,b are in AP then abc, abd, acd, bcd are,
(a). not in AP/GP/HP
(b). in AP
(b). in GP
(d). in HP

• let a simple A.P. a,b,c,d==> 1,2,3,4
  Calculate abc=6 , abd=8, acd=12, bcd=24
  6,8,12,24 are in H.P.
• 10 years agoHelpfull: Yes(6) No(0)
• a,b,c,d in AP
  so 1/bcd,1/acd,1/abd,1/abc will be in AP(divide by abcd)
  so bcd,acd,adb,abc will be in HP
  so abc abd acd bcd are in HP(reverse the series)
  
• 10 years agoHelpfull: Yes(2) No(1)