Đáp án:
`a, S={0;2}`
`b, S={-5;3}`
Giải thích các bước giải:
`a, x⁴ -2x³ +10x² -20x=0`
`<=> x³(x -2)+10x(x-2)=0`
`<=> (x³+10x)(x-2)=0`
`<=> x(x²+10)(x-2)=0`
`<=>` \(\left[ \begin{array}{l}x=0\\x²+10=0\\x-2=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=0\\x²=-10 \ (vô lí) \\x=2\end{array} \right.\)
Vậy `S={0;2}`
`b, 15-2x -x² =0`
`<=> x² +2x -15=0`
`<=> x² +5x -3x -15=0`
`<=> x(x+5) -3(x+5)=0`
`<=> (x+5)(x-3)=0`
`<=>` \(\left[ \begin{array}{l}x+5=0\\x-3=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=-5\\x=3\end{array} \right.\)
Vậy `S={-5;3}`
