If (a+ib)(c+id)(e+if)(g+ih)=A+iB, then prove that (a2+b2)(c2+d2)(e2+f2)(g2+h2)=A2+B2.
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Solution
(a+ib)(c+id)(e+if)(g+ih)=A+iB ∴|(a+ib)(c+id)(e+if)(g+ih)|=|A+iB| or |(a+ib)|×|(c+id)|×|(e+if)|×|(g+ih)|=|A+iB| or √a2+b2×√c2+d2×√e2+f2×√g2+h2=√A2+B2 On squaring both sides, we get (a2+b2)(c2+d2)(e2+f2)(g2+h2)=A2+B2