Đáp án + Giải thích các bước giải:
a, `8x^3-50x=0`
`<=> 2x(4x^2-25) = 0`
`<=> 2x(2x+5)(2x-5) = 0`
`<=>` \(\left[ \begin{array}{l}2x=0\\2x+5=0\\2x-5=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=0\\x=-\dfrac52\\x=\dfrac52\end{array} \right.\)
Vậy `S = {-5/2,5/2,0}`
b, `x^3-x^2-x+1=0`
`<=> -(x-1)+x^2(x-1) = 0`
`<=> (x-1)(x^2-1) = 0`
`<=> (x-1)^2(x+1) = 0`
`<=>`\(\left[ \begin{array}{l}x-1=0\\x+1=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=1\\x=-1\end{array} \right.\)
Vậy `S = {-1,1}`
c, `4x^2-25-(2x+5)(2x+7) = 0`
`<=> 4x^2 - (2x+5)(2x+7) = 25`
`<=> 4x^2 - 4x^2 - 24x - 35 = 25`
`<=> -24x - 35 = 25`
`<=> -24x = 60`
`<=> x = -5/2`
Vậy `S = {-5/2}`
