The given expression is,
( a+ib )( c+id )( e+if )( g+ih )=A+iB
By taking modulus on both the sides, we get
| ( a+ib )( c+id )( e+if )( g+ih ) |=| A+iB | [ ∵| a×b |=| a |×| b | ] | ( a+ib ) |×| ( c+id ) |×| ( e+if ) |×| ( g+ih ) |=| A+iB |
Simplify the above expression,
a 2 + b 2 × c 2 + d 2 × e 2 + f 2 × g 2 + h 2 = A 2 + B 2
By squaring both sides, we get
( a 2 + b 2 )( c 2 + d 2 )( e 2 + f 2 )( g 2 + h 2 )= A 2 + B 2
Hence, the expression has been proved.
If (a+ib)(c+id)(e+if)(g+ih)=A+iB, then (a2+b2)(c2+d2)(e2+f2)(g2+h2)=