(a) 0
Let h be the first term and k be the common ratio of a GP, then
a = hkp – 1, b = hkq – 1, c = hkr – 1
∴ (q – r) log a + (r – p) log b + (p – q) log c
= log [hkp –1]q – r + log [hkq –1]r – p + log[hkr –1]p – q
= log(hq – r + r – p + p – q) (kp – 1)q – r (kq –1)r – p (kr –1)p – q
= log(ho ko) = log 1 = 0.