Phương trình $\dfrac{1}{{{{\log }_2}x}} + \dfrac{1}{{{{\log }_3}x}} + ... + \dfrac{1}{{{{\log }_{2019}}x}} = 2$ có nghiệm thỏa mãn điều kiện nào dưới đây?

$\left\{\begin{array}{l}x = \dfrac{1}{3} - 5t\\y =  - \dfrac{1}{3} - 4t\\z = 3t\end{array}\right.$

$\left\{ \begin{array}{l}x = \dfrac{1}{3} + 5t\\y =  - \dfrac{1}{3} - 4t\\z = 3t\end{array} \right.$

$\left\{ \begin{array}{l}x = \dfrac{1}{3} + 5t\\y =  - \dfrac{1}{3} + 4t\\z = 3t\end{array} \right.$

$\left\{ \begin{array}{l}x = \dfrac{1}{3} - 5t\\y = - \dfrac{1}{3} - 4t\\z =  - 3t\end{array} \right.$

${S_{xq}} = \dfrac{1}{3}\pi rl$

${S_{xq}} = \pi {r^2}l$

${S_{xq}} = \pi rl + \pi {r^2}$

${S_{xq}} = \pi rl$

$\dfrac{{{a^3}\sqrt 3 }}{2}$

$\dfrac{{{a^3}\sqrt 3 }}{3}$          

${a^3}\sqrt 3$           

$\dfrac{{3{a^3}\sqrt 3 }}{2}$

$y = {x^3} + 3x + 2$

$y = {x^3} - 3x + 2$

$y = {x^4} + 3{x^2} + 2$

$y = \dfrac{{x - 1}}{{x + 1}}$

$(S):{(x + 1)^2} + {(y + 1)^2} + {z^2} = 65.$           

$(S):{(x + 1)^2} + {(y - 1)^2} + {z^2} = 9.$

$(S):{(x - 1)^2} + {(y + 2)^2} + {z^2} = 64.$

$(S):{(x + 1)^2} + {(y - 1)^2} + {(z + 2)^2} = 65.$ 

$f'\left( x \right) \ge 0,\forall x \in R.$         

$f'\left( x \right) = 0,\forall x \in R$

$f'\left( x \right) < 0,\forall x \in R.$

$f'\left( x \right) \le 0,\forall x \in R.$

$F\left( x \right) = x\sin x - \cos x + C.$

$F\left( x \right) = {\rm{\;}} - x\sin x - \cos x + C.$

$F\left( x \right) = x\sin x + \cos x + C.$

$F\left( x \right) = {\rm{\;}} - x\sin x + \cos x + C.$