The value of nCr + 2 nCr – 1 + nCr – 2, 2 ≤ r ≤ n, is ____________.
nCr + 2nCr−1 + nCr−2
= nCr + nCr−1 + nCr−1 + nCr−2
= n+1Cr + n+1Cr−1
= n+2Cr using identity
∴ nCr + 2 nCr−1 + nCr−2 = n+2C2
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