Khai triển \(\dfrac{1}{9}{x^2} - \dfrac{1}{{64}}{y^2}\) theo hằng đẳng thức ta được

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

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

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

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

\({\left( {x + 2y} \right)^2} = {x^2} + 4xy + 4{y^2}\).

\({\left( {x - 2y} \right)^2} = {x^2} - 4xy + 4{y^2}\).

\({\left( {x - 2y} \right)^2} = {x^2} - 4{y^2}\).

\(\left( {x - 2y} \right)\left( {x + 2y} \right) = {x^2} - 4{y^2}\).

\(\dfrac{{{x^2}}}{4} - xy + 4{y^2}\)

\(\dfrac{{{x^2}}}{4} - 2xy + 4{y^2}\)

\(\dfrac{{{x^2}}}{4} - 2xy + 2{y^2}\)

\(\dfrac{{{x^2}}}{2} - 2xy + 2{y^2}\)

\({\left( {5x - 2y} \right)^2}\)

\({\left( {2x - 5y} \right)^2}\)

\({\left( {25x - 4y} \right)^2}\)

\({\left( {5x + 2y} \right)^2}\)

\(4 - {\left( {a + b} \right)^2} = \left( {2 + a + b} \right)\left( {2 - a + b} \right)\).

\(4 - {\left( {a + b} \right)^2} = \left( {4 + a + b} \right)\left( {4 - a - b} \right)\).

\(4 - {\left( {a + b} \right)^2} = \left( {2 + a - b} \right)\left( {2 - a + b} \right)\).

\(4 - {\left( {a + b} \right)^2} = \left( {2 + a + b} \right)\left( {2 - a - b} \right)\).

\( 342\)

\(243\)

\(324\)

\( - 324\)