Đáp án+Giải thích các bước giải:

 `a)`

`A=(5x+5)^{2}+10.(x-3).(1+x)+x^{2}-6x+9`

`=[5.(x+1)]^{2}+2.5.(x+1).(x-3)+(x^{2}-2.x.3+3^{2})`

`=(5x+5)^{2}+2.5.(x+1).(x-3)+(x-3)^{2}`

`=(5x+5+x-3)^{2}`

`=(6x+2)^{2}`

Vậy `A=(6x+2)^{2}`

`b)`

`B=\frac{(x-1)^{2}}{4}+x^{2}-1+(x+1)^{2}`

`=[1/2. (x-1)]^{2}+2. 1/2. (x-1).(x+1)+(x+1)^{2}`

`=(1/2x-1/2+x+1)^{2}`

`=(3/2x-1/2)^{2}`

`=(\frac{3x-1}{2})^{2}`

Vậy `B=(\frac{3x-1}{2})^{2}`

`c)`

`C=(x-y-z)^{2}+2.(x-y-z).(y+z)+(y+z)^{2}`

`=(x-y-z+y+z)^{2}`

`=x^{2}`

Vậy `C=x^{2}`