Đáp án `+` Giải thích các bước giải `!`
`2.`
`a)`
`x(x^2+x+1)-x^2(x+1)-2x+5 = 2`
`<=> x^3+x^2+x-x^3-x^2-2x+5 = 2`
`<=> (x^3-x^3)+(x^2-x^2)+(x-2x)+5 = 2`
`<=> -x = -3`
`<=> x = 3`
Vậy `S= {3}`
`b)`
`(x+2)(x^2-2x+4)-x(x^2-2) = 15`
`<=> x^3+8-x^3+2x = 15`
`<=> (x^3-x^3)+2x+8 = 15`
`<=> 2x = 7`
`<=> x = 7/2`
Vậy `S= {7/2}`
`c)`
`2(x^2-4)-(x+5)(2x+1) = 9`
`<=> 2x^2-8-2x^2-x-10x-5 = 9`
`<=> (2x^2-2x^2)+(-x-10x)+(-8-5) = 9`
`<=> -11x-13 = 9`
`<=> -11x = 22`
`<=> x = -2`
Vậy `S= {-2}`
`3.`
`a)`
`x(2x^2-3)-x^2(5x+1)+x^2`
`= 2x^3-3x-5x^3-x^2+x^2`
`= (2x^3-5x^3)+(-x^2+x^2)-3x`
`= -3x^3-3x`
`b)`
`3x(x-2)-5x(1-x)-8(x^2-3)`
`= 3x^2-6x-5x+5x^2-8x^2+24`
`= (3x^2+5x^2-8x^2)+(-6x-5x)+24`
`= -11x+24`
