`a)`
`4x^2+4x+1`
` = (2x)^2+ 2 . 2x . 1 + 1^2`
` = (2x+1)^2`
`b)`
`x^2 + 16 -8x`
` = x^2 - 2 . x . 4 + 4^2`
` =(x-4)^2`
`c)`
`x^2 - x + 1/4`
` = x^2 - 2 . x . 1/2 +(1/2)^2`
` =(x-1/2)^2`
`d)`
`4x^2 y^4 - 12xy^2 + 9`
`= (2xy^2)^2 - 2 . 2xy^2 . 3 + 3^2`
` = (2xy^2 -3)^2`