`x^2 - 10x + 25 - y^2 - 4yz - 4z^2`
`= ( x^2 - 10x + 25 ) - ( y^2 + 4yz + 4z^2 )`
`= ( x^2 - 2 . x . 5 + 5^2 ) - [ y^2 + 2 . y . 2z + ( 2z )^2 ]`
`= ( x - 5 )^2 - ( y + 2z )^2`
`= [ ( x - 5 ) - ( y + 2z ) ] [ ( x - 5 ) + ( y + 2z ) ]`
`= ( x - 5 - y - 2z ) ( x - 5 + y + 2z )`