Đáp án + Giải thích các bước giải:
CT: `(A+-B)^2=A^2+-2AB+B^2`
`A^2-B^2=(A-B)(A+B)`
`a)(x+y+z)^2-2(x+y+z)(y-z)+(y-z)^2`
`=[(x+y+z)-(y-z)]^2`
`=(x+y+z-y+z)^2=(x+2z)^2`
`b)(x+y+z)^2-(y-z)^2`
`=[(x+y+z)-(y-z)][(x+y+z)+(y-z)]`
`=(x+y+z-y+z)(x+y+z+y-z)`
`=(x+2z)(z+2y)`
c)(x+3)^2+4(x+3)+4`
`=(x+3)^2+2.(x+3).2+2^2`
`=(x+3+2)^2=(x+5)^2`
`d)25+10(x+1)+(x+1)^2`
`=5^2+2.5.(x+1)+(x+1)^2`
`=(5+x+1)^2=(x+6)^2`
`e)(x+2)^2+2(x+2)(x-2)+(x-2)^2`
`=(x+2+x-2)^2`
`=(2x)^2=4x^2`
`f)-2(x^2-9)+(x+3)^2`
`=-2(x-3)(x+3)+(x+3)^2`
`=(x+3)[-2(x-3)+x+3]`
`=(x+3)(-2x+6+x+3)`
`=(x-3)(-x+9)`
