જો {C_r} એ ^n{C_r} માટે વપરાતું હોય,તો શ્રેણી | vedclass

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(D) ધારો કે $S = \sum_{r=0}^{n} (-1)^r (r+1) C_r^2$. આપણે જાણીએ છીએ કે યુગ્મ $n$ માટે $\sum_{r=0}^{n} (-1)^r C_r^2 = (-1)^{n/2} \frac{n!}{(n/2)!(n/2)!

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${( - 1)^{n/2}}(n + 2)$

Vedclass · Answer

(D) ધારો કે $S = \sum_{r=0}^{n} (-1)^r (r+1) C_r^2$. આપણે જાણીએ છીએ કે યુગ્મ $n$ માટે $\sum_{r=0}^{n} (-1)^r C_r^2 = (-1)^{n/2} \frac{n!}{(n/2)!(n/2)!}$. તેમજ,$\sum_{r=0}^{n} (-1)^r r C_r^2 = (-1)^{n/2} \frac{n}{2} \frac{n!}{(n/2)!(n/2)!}$. તેથી,$S = \sum_{r=0}^{n} (-1)^r C_r^2 + \sum_{r=0}^{n} (-1)^r r C_r^2$. $S = (-1)^{n/2} \frac{n!}{(n/2)!(n/2)!} + (-1)^{n/2} \frac{n}{2} \frac{n!}{(n/2)!(n/2)!}$. $S = (-1)^{n/2} \frac{n!}{(n/2)!(n/2)!} (1 + n/2) = (-1)^{n/2} \frac{n!}{(n/2)!(n/2)!} \frac{n+2}{2}$. $\frac{2(n/2)!(n/2)!}{n!}$ વડે ગુણતા,આપણને મળે: $\frac{2(n/2)!(n/2)!}{n!} 	imes (-1)^{n/2} \frac{n!}{(n/2)!(n/2)!} \frac{n+2}{2} = (-1)^{n/2}(n+2)$.

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$-{ }^{15}C_{1} 2 \cdot { }^{15}C_{2} - 3 \cdot { }^{15}C_{3} \ldots - 15 \cdot { }^{15}C_{15} { }^{14}C_{1} { }^{14}C_{3} { }^{14}C_{5} \ldots { }^{14}C_{11}$ ની કિંમત શોધો.

$\sum\limits_{r = 0}^{n - 1} {\frac{{^n{C_r}}}{{^n{C_r} + {\,^n}{C_{r + 1}}}}} $ નું મૂલ્ય શું થાય?

ધારો કે $\alpha = \sum_{k=0}^n \left( \frac{({ }^n C_k)^2}{k+1} \right)$ અને $\beta = \sum_{k=0}^{n-1} \left( \frac{{ }^n C_k \cdot { }^n C_{k+1}}{k+2} \right)$. જો $5 \alpha = 6 \beta$ હોય,તો $n$ ની કિંમત શોધો:

જો $(1 + x + x^2)^n = a_0 + a_1x + a_2x^2 + \dots + a_{2n}x^{2n}$ હોય,તો $a_0 + a_3 + a_6 + \dots =$

$\frac{{^nC_0}}{1} + \frac{{^nC_2}}{3} + \frac{{^nC_4}}{5} + \frac{{^nC_6}}{7} + \dots = $

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