Đáp án+Giải thích các bước giải:
`9)(x^2+1)^2-6(x^2+1)+9`
`=(x^2+1-3)^2`
`=(x^2-2)^2`
`10)9(x+5)^2-(x+7)^2`
`=[3(x+9)-(x+7)][3(x+9)+(x+7)]`
`=(3x+27-x-7)(3x+27+x+7)`
`=(2x+20)(4x+34)`
`=4(x+10)(2x+17)`
`11)36-12x+x^2`
`=6^2-2.6.x+x^2`
`=(6-x)^2`
`12)4x^2+12x+9`
`=(2x)^2+2.2x.3+3^2`
`=(2x+3)^2`
`14)1/4x^2-5xy+25y^2`
`=(1/2 x)^2-2.1/2 x.5y+(5y)^2`
`=(1/2 x+5y)^2`
`15)(x-5)^2-16`
`=(x-5)^2-4^2`
`=(x-5-4)(x-5+4)`
`=(x-9)(x-1)`
`16)25-(3-x)^2`
`=5^2-(3-x)^2`
`=(5-3+x)(5+3-x)`
`=(2+x)(8-x)`
`17)(7x-4)^2-(2x+1)^2`
`=(7x-4-2x-1)(7x-4+2x+1)`
`=(5x-5)(9x-3)`
`=15(x-1)(3x-1)`
`18)49(y-4)^2-9(y+2)^2`
`=[7(y-4)]^2-[3(y+2)]^2`
`=[7(y-4)-3(y+2)][7(y-4)+3(y+2)]`
`=(7y-28-3y-6)(7y-28+3y+6)`
`=(4y-34)(10y-22)`
`=4(2y-17)(5y-11)`
`19)8x^3+1/(27)`
`=(2x)^2+(1/3)^3`
`=(2x+1/3)(4x^2-2/3 x+1/9)`
`20)125-x^6`
`=5^3-(x^2)^3`
`=(5-x^2)(25+5x^2+x^4)`
