`m,xz-yz-x^2 +2xy-y^2`

`=z(x-y)-(x^2 -2xy+y^2)`

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

`=(x-y)[z-(x-y)`

`=(x-y)(z-x+y)`

`p,x^2 +8x+15`

`=x^2 +3x+5x+15`

`=x(x+3)+5(x+3)`

`=(x+3)(x+5)`

`k,x^2 -x-12`

`=x^2 -4x+3x-12`

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

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

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

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

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

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

`=0+4ab+0`

`=4ab`

Ta có:
`42=2.3.7`

`70=2.5.7`

`180=2^2 .3^2 .5`

`=> BCNN(42,70,180)=2^2 .3^2 .5.7=1260`

Ta có:
`42=2.3.7`

`70=2.5.7`

`180=2^2 .3^2 .5`

`=> BCNN(42,70,180)=2^2 .3^2 .5.7=1260`

.-.

`x^2 -5x+6=0`

`<=> x^2  -2x -3x+6=0`

`<=>x(x-2)-3(x-2)=0`

`<=>(x-2)(x-3)=0`

\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x-3=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=2\\x=3\end{matrix}\right.\)

Vạy pt có tập nghiệm `S={2;3}`

cho bài toán khác ko có trên mạng cho nhanh