`#AkaShi`
Ví dụ `2`:
`1-4x+4x^2`
`=1^2-2*1*2x+(2x)^2`
`=(1-2x)^2`
.....................
`4x^4-4x^2+1`
`=(2x^2)^2-2*2x^2*1+1^2`
`=(2x^2-1)^2`
$\text{_________________________________}$
Ví dụ `3` :
`81-y^4`
`=9^2-(y^2)^2`
`=(9-y^2)(9+y^2)`
`=[3^2-(y)^2](9+y^2)`
`=(3-y)(3+y)(9+y^2`
........................
`(x+y+z)^2-(x-y-z)^2`
`=[x+y+z-(x-y-z)](x+y+z+z-y-z)`
`=(x+y+z-x+y+z)(x+y+z+x-y-z)`
`=[(x-x)+(y+y)+(z+z)][(x+x)+(y-y)+(z-z)]`
`=(2y+2z)2x`
`=2x*(2y+2z)`
`=2x*2*(y+z)`
`=4x(y+z)`
.......................
Áp dụng HĐT:
`A^2-B^2=(A+B)(A-B)`
`(A-B)^2=A^2-2AB+B^2`
