Đáp án+Giải thích các bước giải:
a.
`(3x+1)^2-(3x-1)^2`
`=(3x+1-3x+1)(3x+1+3x-1)`
`=2.6x`
`=12x`
`=12.50`
`=600`
b.
`x(x-y)-y(x-y)^2+xy^2-x^2y`
`=x(x-y)-y(x-y)^2+xy(y-x)`
`=x(x-y)-y(x-y)^2-xy(x-y)`
`=x(x-y)-[y(x-y)](x-y)-xy(x-y)`
`=x(x-y)-(xy-y^2)(x-y)-xy(x-y)`
`=(x-xy+y^2-xy)(x-y)`
`=(y^2-2xy+x)(x-y)`
`=(15^2-2.115.15+115)(115-15)`
`=-3110.100`
`=-311000`
c.
`x^2+4xy+4y^2-x-2y`
`=(x^2+4xy+4y^2)-(x+2y)`
`=(x+2y)^2-(x+2y)`
`=(x+2y)(x+2y-1)`
`=(4+2.3)(4+2.3-1)`
`=10.9`
`=90`
