यदि $n$ एक धनात्मक पूर्णांक है,तो $\sum_{r=1}^n r \cdot C_r =$

  • A
    $2^{n-1}$
  • B
    $n 2^{n-1}$
  • C
    $n 2^{n+1}$
  • D
    $2^{n+1}$

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यदि $n \geq 2$ एक धनात्मक पूर्णांक है,तो श्रेणी ${}^{n+1} C_{2}+2\left({}^{2} C_{2}+{}^{3} C_{2}+{}^{4} C_{2}+\ldots+{}^{n} C_{2}\right)$ का योग ...... है।

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