$^{4n}{C_0} + {\,^{4n}}{C_2}{x^2} + {\,^{4n}}{C_4}{x^4} + … + {\,^{4n}}{C_{4n}}{x^{4n}}$

$ = \frac{1}{2}[{(1 + x)^{4n}} + {(1 – x)^{4n}}]$

$x = 1$ एवं $x = i$ रखने पर,

$^{4n}{C_0} + {\,^{4n}}{C_2} + {\,^{4n}}{C_4} + … + {\,^{4n}}{C_{4n}} = \frac{1}{2}[{2^{4n}}]$

एवं $^{4n}{C_0} – {\,^{4n}}{C_2} + {\,^{4n}}{C_4} – … + {\,^{4n}}{C_{4n}}$=$\frac{1}{2}[{(1 + i)^{4n}} + {(1 – i)^{4n}}]$

इस प्रकार,  $2{[^{4n}}{C_0} + {\,^{4n}}{C_4} + … + {\,^{4n}}{C_{4n}}]$

$ = {2^{4n – 1}} + \frac{1}{2}{[{(1 + i)^{4n}} + (1 – i)]^{4n}}$

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

$ + {\left[ {\sqrt 2 \left( {\cos \frac{\pi }{4} – i\sin \frac{\pi }{4}} \right)} \right]^{4n}}$

$ = {2^{2n}}(\cos n\pi  + i\sin n\pi ) + {2^{2n}}(\cos n\pi  – i\sin n\pi )$

$ = {2^{2n + 1}}\cos n\pi  = {2^{2n + 1}}{( – 1)^n}$

$\therefore $$2{[^{4n}}{C_0} + {\,^{4n}}{C_4} + … + {\,^{4n}}{C_{4n}}] = {2^{4n – 1}} + \frac{1}{2}{2^{2n + 1}}{( – 1)^n}$

$⇒^{4n}{C_0} + {\,^{4n}}{C_4} + … + {\,^{4n}}{C_{4n}} = {2^{4n – 2}} + {( – 1)^n}{2^{2n – 1}}$

ट्रिक : $n = 1, 2$ रखकर जांच कीजिये