If a, b, c, d are in H.P,, then ab + bc + cd is equal to
3 ad
(a+b) (c+d)
ac
None of these
b = 2aca+c and c = 2bdb+d
∴ (a+c)(b+d) = 2acb.2bdc = 4ad
⇒ ab + bc + cd = 3ad
If a, b, c, d are in H.P., then ab + bc + cd is equal to