If (a+ib)(c+id)(e+if)(g+ih)=A+iB, then (a2+b2)(c2+d2)(e2+f2)(g2+h2)=
A2+B2
(a+ ib)(c+id)(e + if)(g + ih)= A + iB .......(i)
⇒ (a - ib)(c - id)(e - if)(g + ih) = A - iB ........(ii)
Multiplying (i) and (ii), we get
(a2+b2)(c2+d2)(e2+f2)(g2+h2) = A2 + B2