Đáp án `+` Giải thích các bước giải `!`
`a)`
`(2x-1)^3+13(x-1)(x+1) = 14x-13`
`<=> 8x^3-12x^2+6x-1+13(x^2-1) = 14x-13`
`<=> 8x^3-12x^2+6x-1+13x^2-13-14x+13 = 0`
`<=> 8x^3+(-12x^2+13x^2)+(6x-14x)+(-1-13+13) = 0`
`<=> 8x^3+x^2-8x-1 = 0`
`<=> (8x^3-8x)+(x^2-1) = 0`
`<=> 8x(x^2-1)+(x^2-1) = 0`
`<=> (8x+1)(x^2-1) = 0`
`⇔` \(\left[ \begin{array}{l}8x+1=0\\x^2-1=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}8x=-1\\x^2=1\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=-\dfrac{1}{8}\\x=1\\x=-1\end{array} \right.\)
Vậy `S= {-(1)/8; 1; -1}`
`b)`
`(x+2)^3-x(x+1)(x-1) = 6x^2-5x+3`
`<=> x^3+6x^2+12x+8-x(x^2-1) = 6x^2-5x+3`
`<=> x^3+6x^2+12x+8-x^3+x-6x^2+5x-3 = 0`
`<=> (x^3-x^3)+(6x^2-6x^2)+(12x+x+5x)+(8-3) = 0`
`<=> 18x+5 = 0`
`<=> 18x = -5`
`<=> x = -(5)/(18)`
Vậy `S= {-(5)/(18}}`
