Đáp án:
`2)x²y^4-6abxy²+9a²b²`
`6)25x²+20xy+4y²`
`10)x²+8/3xy²+16/9y^4`
`14)8x³-36x²y+54xy²-27y³`
`18)8x³+36x²y+54xy²+27y³`
Giải thích các bước giải:
`2)(y²x-3ab)^2`
`=(xy²)^2-2.xy².3ab+(3ab)^2`
`=x²y^4-6abxy²+9a²b²`
Áp dụng HĐT:`(A-B)²=A²-2AB+B²`
`6)(5x+2y)²`
`=(5x)²+2.5x.2y+(2y)²`
`=25x²+20xy+4y²`
Áp dụng HĐT:`(A+B)²=A²+2AB+B²`
`10)(x+4/3y^2)^2`
`=x²+2.x. 4/3y²+(4/3y^2)^2`
`=x²+8/3xy²+16/9y^4`
Áp dụng HĐT:`(A+B)²=A²+2AB+B²`
`14)(2x-3y)³`
`=(2x)³-3.(2x)².3y+3.2x.(3y)²-(3y)³`
`=8x³-36x²y+54xy²-27y³`
Áp dụng HĐT:`(A-B)³=A³-3A²B+3AB²-B³`
`18)(2x+3y)³`
`=(2x)³+3.(2x)².3y+3.2x.(3y)²+(3y)³`
`=8x³+36x²y+54xy²+27y³`
Áp dụng HĐT:`(A+B)³=A³+3A²B+3AB²+B³`
