[gon]

http://www.wolframalpha.com/input/?i=expand[%281%2Bx%2Bx^2%2F2!%29%281%2Bx%29%281%2Bx%29%281%2Bx%29]

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ส.ป.ส ของ $\frac{x^3}{3!} = 3! \times \frac{11}{2} = 33$