Đáp án + Giải thích các bước giải:
`e)4x^2-4x+1=(2x)^2-2.2x.1+1^2=(2x-1)^2`
`h)25x^2+5x+1/4=(5x)^2+2.5x.1/2+(1/2)^2`
`=(5x+1/2)^2`
i)a^2x^2+1+2ax=(ax)^2+2.ax.1+1^2=(ax+1)^2`
j)25m^2+40mn+16n^2=(5m)^2+2.5m.4n+(4n)^2`
`=(5m+4n)^2`
`k)4a^2x^2+b^2-4abx=(2ax)^2-2.2ax.b+b^2`
`=(2ax-b)^2`
`l)(a^2)/(9)-2/(15) ab+(b^2)/(25)`
`=1/9a^2-2/(15)ab+1/(25)b^2`
`=(1/3a)^2-2.1/3a.1/5b+(1/5b)^2`
`=(1/3a-1/5b)^2`
