If a, b and c are in G.P., then b−ab−c+b+ab+c=
If a, b, c, d are in G.P., prove that :
(i) ab−cdb2−c2=a+cb
(ii) (a+b+c+d)2=(a+b)2+2(b+c)2+(c+d)2
(iii) (b+c)(b+d)=(c+d)(c+d)