Đáp án + Giải thích các bước giải:
`25.` `(p-2q)^2-4(p+q)^2`
`=(p-2q)^2-[2(p+q)]^2`
`=(p-2q)^2-(2p+2q)^2`
`=[(p-2q)-(2p+2q)][(p-2q)+(2p+2q)]`
`=(p-2q-2p-2q)(p-2q+2p+2q)`
`=(-p-4q)*3q`
`26.` `25p^2m^4-1/36p^4`
`=(5p m^2)^2-(1/6p^2)^2`
`=(5p m^2-1/6p^2)(5p m^2+1/6p^2)`
`27.` `16x^2-9(x+y)^2`
`=(4x)^2-[3(x+y)]^2`
`=(4x)^2-(3x+3y)^2`
`=[4x-(3x+3y)][4x+(3x+3y)]`
`=(4x-3x-3y)(4x+3x+3y)`
`=(x-3y)(7x+3y)`
`28.` `x^2+6xy^2+9y^4`
`=9y^4+6xy^2+x^2`
`=(3y^2)^2+2*3y^2*x+x^2`
`=(3y^2+x)^2`
`29.` `x^6+y^2-2x^3y`
`=x^6-2x^3y+y^2`
`=(x^3)^2-2*x^3*y+y^2`
`=(x^3-y)^2`
`30.` `36p^4+12p^2q^2+q^4`
`=(6p^2)^2+2*6p^2*q^2+(q^2)^2`
`=(6p^2+q^2)^2`
`31.` `x^2+2x+1=(x+1)^2`
`32.` `-a^2-2a-1=-(a^2+2a+1)=-(a+1)^2`
`33.` `9m^6+24m^3n^2+16n^4`
`=(3m^3)^2+2*3m^3*4n^2+(4n^2)^2`
`=(3m^3+4n^2)^2`
`34.` `25x^4-10x^2y^2+y^4`
`=(5x^2)^2-2*5x^2*y^2+(y^2)^2=(5x^2-y^2)^2`
`35.` `4a^4-4a^2b^2+b^4`
`=(2a^2)^2-2*2a^2*b^2+(b^2)^2=(2a^2-b^2)^2`
`36.` `-y^8+10y^4x^3-25x^6`
`=-(y^8-10y^4x^3+25x^6)`
`=-[(y^4)^2-2*y^4*5x^3+(5x^3)^2]`
`=-(y^4-5x^3)^2`.
