Câu `1`
`a)(x-3)(x+3)(x^2+9)`
`=(x^2-9)(x^2+9)`
`=x^4-81`
`b)(y+2z-3)(y-2z-3)`
`=[(y-3)+2z][(y-3)-2z]`
`=(y-3)^2-(2z)^2`
`=y^2-6y+9-4z^2`
Câu `2`
`a)100a^2-1=(10a+1)(10-1)`
`b)25x^2-16y^2=(5x+4y)(5x-4y)`
`c)x^2-49=(x+7)(x-7)`
`d)x^8-y^8`
`=(x^4)^2-(y^4)^2`
`=(x^4+y^4)(x^4-y^4)`
`=(x^4+y^2)[(x^2)^2-(y^2)^2]`
`=(x^4+y^2)(x^2+y^2)(x^2-y^2)`
`=(x^4+y^2)(x^2+y^2)(x+y)(x-y)`
`e)16x^4-81`
`=(4x^2)^2-9^2`
`=(4x^2+9)(4x^2-9)`
`=(4x^2+9)(2x+3)(2x-3)`