phân tích đa thức thành nt a, 3x^2-3y^2-12x+12y b,25-x^2+6xy-9y^2

Hướng dẫn trả lời:

`a)3x^2-3y^2-12x+12y.`

`=(3x^2-3y^2)-(12x-12y).`

`=3.(x^2-y^2)-12.(x-y).`

`=3.(x+y).(x-y)-12.(x-y).`

`=(x-y).[3.(x+y)-12].`

`=(x-y).3.[(x+y)-4].`

`=(x-y).3.(x+y-4).`

`b)25-x^2+6xy-9y^2.`

`=25-(x^2-6xy+9y^2).`

`=5^2-[x^2-2.x.3y+(3y)^2].`

`=5^2-(x-3y)^2.`

`=[5+(x-3y)].[5-(x-3y)].`

`=(x-3y+5).(-x+3y+5).`