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Question

Question: If (1 + i) (1 + 2i) (1 + 3i) .....(1 + ni) = a + ib, then 2.5, 10, .....(1 + n<sup>2</sup>) =...

If (1 + i) (1 + 2i) (1 + 3i) .....(1 + ni) = a + ib, then 2.5, 10, .....(1 + n2) =

A

a – ib

B

a2 – b2

C

a2 + b2

D

None of these

Answer

a2 + b2

Explanation

Solution

Sol. Taking modulus both sides

|1+ i| |1 + 2i| |1 + 3i| ......... |1 + ni| |a + ib|

2\sqrt{2}.5\sqrt{5}.10\sqrt{10} ..............1+n2\sqrt{1 + n^{2}} =α2+β2\sqrt{\alpha^{2} + \beta^{2}}

i.e. 2.5.10 .......... (1 + n2) = a2 + b2