Question:

The sum of the series ${^{20}C_0} - {^{20}C_1} + {^{20}C_2} - {^{20}C_3} + ..... - .... + {^{20}C_{10}}$ is

Updated On: Jul 5, 2022
  • 0
  • ${^{20}C_{10}}$
  • ${^{ - 20}C_{10}}$
  • $ \frac{1}{2} {^{20}C_{10}}$
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The Correct Option is D

Solution and Explanation

$\left(1+x\right)^{20}=^{20}C_{0}+^{20}C_{1}x+...+^{20}C_{10}x^{10}+...+^{20}C_{20}x^{20}$ put $x = - 1,$ $0=^{20}C_{0}-^{20}C_{1}+...-^{20}C_{9}+^{20}C_{11}+...+^{20}C_{20}$ $0=2\left(^{20}C_{0}-^{20}C_{1}+...-^{20}C_{9}\right)=^{20}C_{10}$ $\Rightarrow ^{20}C_{0}-^{20}C_{1}+...+^{20}C_{10}=\frac{1}{2}^{20}C_{10}.$
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Concepts Used:

Binomial Theorem

The binomial theorem formula is used in the expansion of any power of a binomial in the form of a series. The binomial theorem formula is 

Properties of Binomial Theorem

  • The number of coefficients in the binomial expansion of (x + y)n is equal to (n + 1).
  • There are (n+1) terms in the expansion of (x+y)n.
  • The first and the last terms are xn and yn respectively.
  • From the beginning of the expansion, the powers of x, decrease from n up to 0, and the powers of a, increase from 0 up to n.
  • The binomial coefficients in the expansion are arranged in an array, which is called Pascal's triangle. This pattern developed is summed up by the binomial theorem formula.