For a, b, c to be in GP, what is the value of a−bb−c
For a, b, c to be in GP, we must have
ba=cb=r or ba=cb=1r
Case I When ba=cb=r
In this case, b = ar and c = br.
∴ a−bb−c=a−arb−br=a(1−r)b(1−r)=ab
Case II When ba=cb=1r
In this case, a = br and b = cr.
∴ a−bb−c=br−bcr−c=b(r−1)c(r−1)=bc
Hence, the value of (a−bb−c) is ab or bc.