`a)(x-9)(x-7)+1`

`=[(x-8)-1][(x-8)+1]+1`

`=(x-8)^2-1^2+1`

`=(x-8)^2-1+1`

`=(x-8)^2`

`b)x^6-y^6`

`=(x^3)^2-(y^3)^2`

`=(x^3-y^3)(x^3+y^3)`

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

`c)(x^2+x-1)^2+4x^2+4x` 

`=(x^2+x)^2-2(x^2+x)+1+4x^2+4x`

`=(x^2+x)^2-2(x^2+x)+1+4(x^2+x)`

`=(x^2+x)^2+2(x^2+x)+1`

`=(x^2+x+1)^2`

1.62:

`a)(x+2y-3)^2-4(x+2y-3)+4`

`=(x+2y-3)^2-2*(x+2y-3)*2+2^2`

`=(x+2y-3-2)^2`

`=(x+2y-5)^2`

`b)(x-y)^3-1-3(x-y)(x-y-1)`

`=(x-y-1)[(x-y)^2+(x-y)+1]-3(x-y)(x-y-1)`

`=(x-y-1)[(x-y)^2+(x-y)+1-3(x-y)]`

`=(x-y-1)[(x-y)^2-2(x-y)+1]`

`=(x-y-1)(x-y-1)^2`

`=(x-y-1)^3`

1.63:

`(x^2+y^2-17)^2-4(xy-4)^2`

`=(x^2+y^2-17)^2-(2xy-8)^2`

`=(x^2+y^2-17-2xy+8)(x^2+y^2-17+2xy-8)`

`=(x^2-2xy+y^2-9)(x^2+2xy+y^2-25)`

`=[(x-y)^2-9][(x+y)^2-5^2]`

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

1.64:

`a)x^3+15x^2+75x+125=0`

`x^3+3*x^2*5+3*x*5^2+5^3=0`

`(x+5)^3=0`

`x+5=0`

`x=-5`

Vậy: `x=-5`

`b)(x+2)^3+(x-3)^3=0`

`(x+2)^3=-(x-3)^3`

`(x+2)^3=(3-x)^3`

`x+2=3-x`

`x+x=3-2`

`2x=1`

`x=1/2`

Vậy: `x=1/2`