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Question Number 12580 by @ANTARES_VY last updated on 26/Apr/17
Find  the  smaillest  value  of  the  sum  x(x+1)(x+2)(x+3).
$$\boldsymbol{\mathrm{Find}}\:\:\boldsymbol{\mathrm{the}}\:\:\boldsymbol{\mathrm{smaillest}}\:\:\boldsymbol{\mathrm{value}}\:\:\boldsymbol{\mathrm{of}}\:\:\boldsymbol{\mathrm{the}} \\ $$$$\boldsymbol{\mathrm{sum}} \\ $$$$\boldsymbol{\mathrm{x}}\left(\boldsymbol{\mathrm{x}}+\mathrm{1}\right)\left(\boldsymbol{\mathrm{x}}+\mathrm{2}\right)\left(\boldsymbol{\mathrm{x}}+\mathrm{3}\right). \\ $$
Answered by ajfour last updated on 26/Apr/17
(x^2 +3x)(x^2 +3x+2)  =(x^2 +3x)^2 +2(x^2 +3x)+1−1  =(x^2 +3x+1)^2 −1  so its smallest value is −1 .
$$\left({x}^{\mathrm{2}} +\mathrm{3}{x}\right)\left({x}^{\mathrm{2}} +\mathrm{3}{x}+\mathrm{2}\right) \\ $$$$=\left({x}^{\mathrm{2}} +\mathrm{3}{x}\right)^{\mathrm{2}} +\mathrm{2}\left({x}^{\mathrm{2}} +\mathrm{3}{x}\right)+\mathrm{1}−\mathrm{1} \\ $$$$=\left({x}^{\mathrm{2}} +\mathrm{3}{x}+\mathrm{1}\right)^{\mathrm{2}} −\mathrm{1} \\ $$$${so}\:{its}\:{smallest}\:{value}\:{is}\:−\mathrm{1}\:. \\ $$
Commented by @ANTARES_VY last updated on 26/Apr/17
6x^3  ?????
$$\mathrm{6}\boldsymbol{\mathrm{x}}^{\mathrm{3}} \:????? \\ $$
Commented by ajfour last updated on 26/Apr/17
what′s wrong???
$${what}'{s}\:{wrong}??? \\ $$

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