giúp mình với

`a,`

`x^2 - 4x + 4 = x^2 - 2x - 2x + 4 = x ( x - 2 ) - 2 ( x - 2 ) = ( x - 2 )(x-2)=(x-2)^2`

`b,`

`9x^2 - 6x + 1 = 9x^2 - 3x - 3x + 1 = 3x ( 3x - 1 ) - 1 ( 3x - 1 ) = ( 3x - 1 )(3x - 1 ) = (3x-1)^2`

`c,`

`x^2 + x + 1/4 = x^2 + 2. 1/2 . x +(1/2)^2 = (x + 1/2)^2`

`d,`

`25x^2 - 10x + 1 = 25x^2 - 5x - 5x + 1 = 5x ( 5x - 1 ) - 1 ( 5x - 1 ) = (5x - 1 ) ( 5x - 1 ) = (5x - 1 )^2`

`e,`

`x^2 + 10x + 25 = x^2 + 5x + 5x + 25 = x ( x + 5 ) + 5 ( x + 5 ) = ( x + 5 ) ( x + 5 ) = ( x + 5 )^2`

`f,`

`x^2 + 3x + 9/4 = x^2 + 2 . 3/2 x + (3/2)^2 = ( x + 3/2 )^2`