a) (1/3x - 1/2y)^2 b) (x/2 - y)(x/2 + y) c) (căn 2x-y)^2

`a) (1/3 x - 1/2 y )^2`

`= (1/3x )^2 -2 . 1/3  x . 1/2 y + (1/2 y)^2`

`= (1/3)^2 . x^2 - (2. 1/3 . 1/2 ) . xy + (1/2)^2 . y^2`

`= 1/9 x^2 - 1/3 xy + 1/4 y^2`

`b) (x/2 -y) . ( x/2 + y)`

`= (x/2)^2 - y^2`

`= (x^2)/(2^2) - y^2`

`= (x^2)/4 - y^2`

`c) ( \sqrt(2) x - y)^2`

`=( \sqrt(2) . x)^2 - 2 . \sqrt(2)x . y + y^2`

`= 2 x^2 - 2 \sqrt(2) . x y+ y^2`