Giá trị của biểu thức $A = 2x\left( {3x - 1} \right) - 6x\left( {x + 1} \right) - \left( {3 - 8x} \right)$ là:

$1 - 2x$

$x - {x^2}$

${x^2} - x$

${x^2} + x$

$12{x^8} + 21{x^5}$

$12{x^8} + 21{x^6}$

$- 12{x^8} + 21{x^5}$

$- 12{x^8} - 21{x^5}$

$A = 4$

$A =  - 4$

$A = 19$

$A =  - 19$

${\left( {4x - \dfrac{1}{2}} \right)^2}$

${\left( {x - \dfrac{1}{2}} \right)^2}$

${\left( {4x + \dfrac{1}{2}} \right)^2}$

${\left( {x + \dfrac{1}{2}} \right)^2}$

${\left( {A + B} \right)^2} = {A^2} + 2AB + {B^2}$

${\left( {A - B} \right)^3} = {A^3} - 3{A^2}B - 3A{B^2} + {B^3}$

${A^2} - {B^2} = \left( {A - B} \right)\left( {A + B} \right)$

${A^3} - {B^3} = \left( {A - B} \right)\left( {{A^2} + AB + {B^2}} \right)$

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