\(\sum_{r=0}^{n}r^2{}^{n}C_r\) का सही रूप क्या है?
What is the correct form of \(\sum_{r=0}^{n}r^2{}^{n}C_r\)?
Explanation opens after your attempt
Correct Answer
C. (n(n+1)2^{n-2})
Concept
Write (r-2=r(r-1)+r) and add two standard sums. In exams splitting \(r^2\) is the fastest method.
Why this answer is correct
The correct answer is C. (n(n+1)2^{n-2}). Write (r-2=r(r-1)+r) and add two standard sums. In exams splitting \(r^2\) is the fastest method.
Exam Tip
(r-2=r(r-1)+r) लिखकर दो standard sums जोड़ते हैं। परीक्षा में \(r^2\) को split करना तेज तरीका है।
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