Find the value of n+1C2 + 2(2C2 + 3C2 + …… + nC2) = ? (1) $n(n+1)(2n-1)\over6$ (2) $n(n+1)(2n+1)\over6$ (3) $(n-1)n(n+1)\over6$ (4) $n(n+1)\over2$

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