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```
20 ∑ r. ( 20 Cr) 2 = ? r=0 Please Give Full explanation
20∑ r. (20Cr)2 = ?r=0 Please Give Full explanation

```
9 months ago

2074 Points
```							note that we have the following property of summation: ∑r=m to n f(r) = ∑r=m to n f(m+n – r)so, let S= ∑ r. (20Cr)2 .....(1)using property S= ∑ (0+20 – r). (20C(0+20 – r))2 but nCr= nC(n-r)so, S= ∑ (20 – r). (20Cr)2 .........(2)add (1) and (2)2S= ∑ 20(20Cr)2 S= 10 ∑ (20Cr)2 now a pretty common result is nc0² + nC1² + nC2² +.......+ nCn² = 2nCn (quite easy to prove, lemme know if you need help).so, we have S= 10*(40C20)KINDLY APPROVE :))
```
9 months ago
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• 101 Video Lectures
• Revision Notes
• Test paper with Video Solution
• Mind Map
• Study Planner
• NCERT Solutions
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• Previous Year Exam Questions