2nCr = 2nCr + 2 হলে r এর মান কত?
Solution
Correct Answer: Option B
2n C r = 2n C r + 2
বা, 2n = r + r + 2 [ n c 5 = n C 7 হলে n = 5 + 7]
বা, r + r = 2n - 2
বা, 2r = 2(n - 1)
বা, r = 2(n - 1)/2
∴ r = (n - 1)
বা, 2n = r + r + 2 [ n c 5 = n C 7 হলে n = 5 + 7]
বা, r + r = 2n - 2
বা, 2r = 2(n - 1)
বা, r = 2(n - 1)/2
∴ r = (n - 1)
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