Đáp án + Giải thích các bước giải:
Bài `4` :
`a)` `(x+y)^2-6(x+y)+9`
`=(x+y)^2-2*(x+y)*3+3^2`
`=(x+y-3)^2`
`b)` `16a^2-49(b-c)^2=(4a)^2-[7(b-c)]^2`
`=(4a)^2-(7b-7c)^2=(4a-7b+7c)(4a+7b-7c)`
`c)` `49(y-4)^2-9(y-2)^2`
`=[7(y-4)]^2-[3(y-2)]^2`
`=(7y-28)^2-(3y-6)^2`
`=(7y-28-3y+6)(7y-28+3y-6)`
`=(4y-22)(10y-34)`
`=(4y-22)*2(5y-17)`
`d)` `10x(x-y)-8y(y-x)`
`=10x(x-y)+8y(x-y)`
`=(x-y)(10x+8y)`
`=(x-y)*2(5x+4y)`
`e)` `5x(x-2000)-x+2000`
`=5x(x-2000)-(x-2000)=(x-2000)(5x-1)`.
