Đáp án + Giải thích các bước giải:
`a)` `(5x-2x)(3x+4y)-(4x+y)^2` $\\$ `= 3x(3x+4y)-[(4x)^2+2*4x*y+y^2]` $\\$ `= 9x^2 + 12xy - (16x^2+8xy+y^2)` $\\$ `= 9x^2+ 12xy - 16x^2 - 8xy - y^2 = -7x^2+4xy-y^2`
`b)` `(3x - 2y)^2+(5x-3y)(3y+5x)` $\\$ `= (3x)^2-2*3x*2y+(2y)^2 - (3y - 5x)(3y + 5x)` $\\$ `= 9x^2-12xy+4y^2-(9y^2-25x^2)` $\\$ `= 9x^2 - 12xy + 4y^2 - 9y^2 + 25x^2 = 34x^2-5y^2-12xy`
`c)` `(x - 1)(x^2 + x + 1)-(x+1)(x^2-x+1)` $\\$ `= x^3 -1 - (x^3+1)=x^3-1-x^3-1=-2`
`d)` `(x + 1)^3-x(x-1)^2+6` $\\$ `=x^3+3x^2+3x+1-x(x^2-2x+1)+6` $\\$ `= x^3 + 3x^2 + 3x + 1 - x^3 + 2x^2 - x + 6` $\\$ `= 5x^2+2x+7`
