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|
2.5.10 ..............1+n2 =α2+β2
i.e. 2.5.10 .......... (1 + n2) = a2 + b2