Tui mới hok đến đẳng thức đáng nhớ thui nha

` a) ( 2x + 1 )^2 `

` = ( 2x )^2 + 2 . 2x . 1 + 1^2 `

` = 4x^2 + 4x + 1 `

` b) ( 3x - 2y )^2 `

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

` = 9x^2 - 12xy + 4y^2 `

` c) ( 3x + 1 )( 3x - 1 )`

` = ( 3x )^2 - 1^2 `

` = 9x^2 - 1 `

 ` d) ( x + 1/6 y + 3 )^2 `

` = x^2 + ( 1/6 y )^2 + 3^2 + 2 . x . 1/6 y + 2 .x . 3 + 2 . 1/6 y . 3` 

` = x^2 + \frac{1}{36} y^2 + 9 + 1/3xy + 6x + y `

` e) ( \sqrt{2} y - 1 )^2 `

` = ( \sqrt{2} y )^2 - 2 . \sqrt{2}y . 1 + 1^2 `

` = 2y^2 - 2\sqrt{2}y + 1 `

` f) ( x/2 + 2y^2 )( x/2 - 2y^2 )`

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

` = \frac{x^2}{4} - 4y^4 `