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CAT 2002 | Question: 73

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Let $S=2x + 5x^2 + 9x^3 + 14x^4 + 20x^5 \dots \dots $ infinity. The coefficient of $n$-th term is$\frac{n(n+3)}{2}$. Then the sum $S$ is

  1. $\frac{x(2-x)}{(1-x)^3}$
  2. $\frac{(2-x)}{(1-x)^3}$
  3. $\frac{x(2-x)}{(1-x)^2}$
  4. None of these
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