Prove The Following Equation C0 2C1 + 3C2 4C3 + + Left ... - Vedantu

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• Prove the following equation C...

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Start with the general formula then make some substitution in the formula according to the problem statement in order to make the series similar to the given one.Complete step-by-step answer:We have to prove ${C_0} - 2{C_1} + 3{C_2} - 4{C_3} + ....... + {\left( { - 1} \right)^n}\left( {n + 1} \right){C_n} = 0$ As we know the general formula for the binomial expansion of the series is given by:\[{\left( {1 + x} \right)^n} = {C_0}{x^0} + {C_1}{x^1} + {C_2}{x^2} + {C_3}{x^3} + ....... + {C_n}{x^n}\] Multiplying both sides of the above equation by x we get:\[ \Rightarrow x \times {\left( {1 + x} \right)^n} = x \times \left( {{C_0}{x^0} + {C_1}{x^1} + {C_2}{x^2} + {C_3}{x^3} + ....... + {C_n}{x^n}} \right) \\ \Rightarrow {\left( {1 + x} \right)^n} \cdot x = {C_0}{x^1} + {C_1}{x^2} + {C_2}{x^3} + {C_3}{x^4} + ....... + {C_n}{x^{n + 1}} \\ \] Now in order bring the equation something in form of the result let us differentiate the whole equation with respect to x\[ \Rightarrow \dfrac{d}{{dx}}\left[ {{{\left( {1 + x} \right)}^n} \cdot x} \right] = \dfrac{d}{{dx}}\left[ {{C_0}{x^1} + {C_1}{x^2} + {C_2}{x^3} + {C_3}{x^4} + ....... + {C_n}{x^{n + 1}}} \right]\] Now let us open the brackets in order to differentiate the whole term\[ \Rightarrow \dfrac{d}{{dx}}\left[ {{{\left( {1 + x} \right)}^n} \cdot x} \right] = \dfrac{d}{{dx}}\left[ {{C_0}{x^1}} \right] + \dfrac{d}{{dx}}\left[ {{C_1}{x^2}} \right] + \dfrac{d}{{dx}}\left[ {{C_2}{x^3}} \right] + \dfrac{d}{{dx}}\left[ {{C_3}{x^4}} \right] + ....... + \dfrac{d}{{dx}}\left[ {{C_n}{x^{n + 1}}} \right]\] As we know the formulas for differentiation are:\[\dfrac{d}{{dx}}\left( {{x^k}} \right) = k{x^{k - 1}}{\text{ and }}\dfrac{d}{{dx}}\left( {p.q} \right) = p\dfrac{d}{{dx}}\left( q \right) + q\dfrac{d}{{dx}}\left( p \right)\] Using the above formulas we differentiate the terms in the equation:\[ \Rightarrow {\left( {1 + x} \right)^n}\dfrac{d}{{dx}}\left( x \right) + x\dfrac{d}{{dx}}\left[ {{{\left( {1 + x} \right)}^n}} \right] = {C_0}\dfrac{d}{{dx}}\left[ {{x^1}} \right] + {C_1}\dfrac{d}{{dx}}\left[ {{x^2}} \right] + ..... \\ .....{C_2}\dfrac{d}{{dx}}\left[ {{x^3}} \right] + {C_3}\dfrac{d}{{dx}}\left[ {{x^4}} \right] + ....... + {C_n}\dfrac{d}{{dx}}\left[ {{x^{n + 1}}} \right] \\ \] As \[{C_0},{C_1},{C_2},.....,{C_n}\] are constants.Proceeding further we get\[ \Rightarrow {\left( {1 + x} \right)^n} \times 1 + x \times n{\left( {1 + x} \right)^{n - 1}} = {C_0} \times 1 + {C_1} \times 2x + {C_2} \times 3{x^2} + {C_3} \times 4{x^3} + ....... + {C_n} \times \left( {n + 1} \right){x^n} \\ \Rightarrow {\left( {1 + x} \right)^n} + n{\left( {1 + x} \right)^{n - 1}}x = {C_0} + 2{C_1}x + 3{C_2}{x^2} + 4{C_3}{x^3} + ....... + \left( {n + 1} \right){C_n}{x^n} \\ \] Now, in order to remove x from the equation and to bring the equation similar to the result we will substitute x = -1 in the above equation.\[ \Rightarrow {\left( {1 + \left( { - 1} \right)} \right)^n} + n{\left( {1 + \left( { - 1} \right)} \right)^{n - 1}}\left( { - 1} \right) = {C_0} + 2{C_1}\left( { - 1} \right) + 3{C_2}{\left( { - 1} \right)^2} + 4{C_3}{\left( { - 1} \right)^3} + ....... + \left( {n + 1} \right){C_n}{\left( { - 1} \right)^n}\] Further evaluating the equation above we get:\[ \Rightarrow {\left( {1 - 1} \right)^n} + n{\left( {1 - 1} \right)^{n - 1}}\left( { - 1} \right) = {C_0} - 2{C_1} + 3{C_2} - 4{C_3} + ....... + \left( {n + 1} \right){C_n}{\left( { - 1} \right)^n} \\ \Rightarrow {C_0} - 2{C_1} + 3{C_2} - 4{C_3} + ....... + \left( {n + 1} \right){C_n}{\left( { - 1} \right)^n} = {\left( 0 \right)^n} + n{\left( 0 \right)^{n - 1}}\left( { - 1} \right) \\ \Rightarrow {C_0} - 2{C_1} + 3{C_2} - 4{C_3} + ....... + {\left( { - 1} \right)^n}\left( {n + 1} \right){C_n} = 0 \\ \] Hence the result is proved and we have \[{C_0} - 2{C_1} + 3{C_2} - 4{C_3} + ....... + {\left( { - 1} \right)^n}\left( {n + 1} \right){C_n} = 0\] .Note: In order to solve such problems students should first try to visualize for some binomial expansion series. Students must not just start with the LHS in order to prove RHS. Students must remember the formula for binomial theorem for series expansion and methods of differentiation in order to solve such problems.Recently Updated PagesA man running at a speed 5 ms is viewed in the side class 12 physics CBSEState and explain Hardy Weinbergs Principle class 12 biology CBSEWhich of the following statements is wrong a Amnion class 12 biology CBSETwo Planoconcave lenses 1 and 2 of glass of refractive class 12 physics CBSEThe compound 2 methyl 2 butene on reaction with NaIO4 class 12 chemistry CBSEBacterial cell wall is made up of A Cellulose B Hemicellulose class 12 biology CBSEA man running at a speed 5 ms is viewed in the side class 12 physics CBSEState and explain Hardy Weinbergs Principle class 12 biology CBSEWhich of the following statements is wrong a Amnion class 12 biology CBSETwo Planoconcave lenses 1 and 2 of glass of refractive class 12 physics CBSEThe compound 2 methyl 2 butene on reaction with NaIO4 class 12 chemistry CBSEBacterial cell wall is made up of A Cellulose B Hemicellulose class 12 biology CBSE

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