MCQ
If $n $ is a positive integer, then ${\left( {\sqrt 3 + 1} \right)^{2n}} - {\left( {\sqrt 3 - 1} \right)^{2n}}$ is
  • an irrational number
  • B
    an odd positive integer
  • C
    an even positive integer
  • D
    a rational number other than positive integers

Answer

Correct option: A.
an irrational number
a
$1+i=\sqrt{2}\left(\cos \frac{\pi}{4}+i \sin \frac{\pi}{4}\right)$

$1-i=\sqrt{2}\left(\cos \left(-\frac{\pi}{4}\right)+i \sin \left(-\frac{\pi}{4}\right)\right)$

$(1+i)^{n}=(\sqrt{2})^{n}\left(\cos \frac{n \pi}{4}+i \sin \frac{n \pi}{4}\right)$

$(1-i)^{n}=(\sqrt{2})^{n}\left(\cos \left(-\frac{n \pi}{4}\right)+i \sin \left(-\frac{n \pi}{4}\right)\right)$

$(1+i)^{n}+(1-i)^{n}=(\sqrt{2})^{n}\left(2 \cos \frac{n \pi}{4}\right)$

$=2^{\frac{n+2}{2}} \cos \frac{n \pi}{4}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free