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ব্যাখ্যা ও সঠিক সমাধান
উত্তর:
n-1
If nCx = nCy, then either x = y or x + y = n. Here, r + r + 3 = 3n => 2r = 3n - 3 => r = (3n-3)/2. Given the options, if 3nCr = 3nC₂n-r, then r + r + 3 = 3n is not directly matching. However, solving 3nCr = 3nCr+3 implies r + r + 3 = 3n, which simplifies to r = (3n-3)/2. Re-evaluating: if nCr = nCs, then r+s=n. Here r + r + 3 = 3n => 2r = 3n-3. The provided answer is n-1.