\(\sum_{r=0}^{n}{}^{n}C_r{}^{n-r}C_m\) का सही सरल रूप कौन-सा है?
What is the correct simplified form of \(\sum_{r=0}^{n}{}^{n}C_r{}^{n-r}C_m\)?
Explanation opens after your attempt
A. \(^{n}C_m2^{n-m}\)
Concept
First place the (m) special members in the second part and give free choices to the remaining (n-m) members. In exams choose the fixed marked set first in such sums.
Why this answer is correct
The correct answer is A. \(^{n}C_m2^{n-m}\). First place the (m) special members in the second part and give free choices to the remaining (n-m) members. In exams choose the fixed marked set first in such sums.
Exam Tip
पहले (m) विशेष सदस्यों को दूसरे भाग में रखिए और बाकी (n-m) सदस्यों को स्वतंत्र विकल्प दीजिए। परीक्षा में ऐसे sums में fixed marked set पहले चुनें।
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