( x-y+6)(x+y-6) (y+2z-3)(y-2z-3) (x+2y-3z)(2y+3z-x)

Đáp án:

`***` Phân tích thành hiệu hai bình phương:

`(x-y+6).(x+y-6)`

`=[x-(y-6)].[x+(y-6)]`

`=x^2-(y-6)^2`

`\text()`

`(y+2z-3).(y-2z-3)`

`=[(y-3)+2z].[(y-3)-2z]`

`=(y-3)^2-(2z)^2`

`\text()`

`(x+2y-3z).(2y+3z-x)`

`=[2y-(3z-x)].[2y+(3z-x)]`

`=(2y)^2-(3z-x)^2`

__________________________

`***`Nếu đề là khai triển:

`(x-y+6).(x+y-6)=[x-(y-6)].[x+(y-6)]`

`=x^2-(y-6)^2`

`=x^2-(y^2-12y+36)`

`=x^2-y^2+12y-36`

`\text( )`

`(y+2z-3).(y-2z-3)=[(y-3)+2z].[(y-3)-2z]`

`=(y-3)^2-(2z)^2`

`=y^2-6x+9-4z^2`

`\text( )`

`(x+2y-3z).(2y+3z-x)=[2y-(3z-x)].[2y+(3z-x)]`

`=(2y)^2-(3z-x)^2`

`=4y^2-(9z^2-6xz+x^2)`

`=4y^2-9z^2+6xz-x^2`

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`***`AD : `(a-b).(a+b)=a^2-b^2`

`(a-b)^2=a^2-2ab+b^2`