Giải thích các bước giải:
`e, (x+2)(3-2x)=0`
⇒\(\left[ \begin{array}{l}x+2=0\\3-2x=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=-2\\x=3/2\end{array} \right.\)
`g, x^2-3x+2=0`
⇒``x^2-x-2x+2=0`
⇒`x(x-1)-2(x-1)=0`
⇒`(x-1)(x-2)=0`
⇒\(\left[ \begin{array}{l}x-1=0\\x-2=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=1\\x=2\end{array} \right.\)
`h, x^3+x^2-x-1=0`
⇒`x^2(x+1)-(x+1)=0`
⇒`(x+1)(x^2-1)=0`
⇒\(\left[ \begin{array}{l}x+1=0\\x^2-1=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}-1\\1\end{array} \right.\)
`i, x^3+1=0`
⇒`x^3=-1`
⇒`x=-1`
`k, x^4+x^3-12x^2=0`
⇒`x^2(x^2+x-12)=0`
⇒`x^2(x(x+4)-3(x+4))=0`
⇒`x^2(x+4)(x-3)=0`
⇒\(\left[ \begin{array}{l}x^2=0\\x+4=0\\x-3=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=0\\x=-4\\x=3\end{array} \right.\)
`m, (x^2+5x)^2-2(x^2+5x)-24=0`
Thay `(x^2+5x)=t`
⇒`t^2-2t-24=0`
⇒\(\left[ \begin{array}{l}t=-4\\t=6\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x^2+5x=-4\\x^2+5x=6\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=-4\\x=-1\\x=-6\\x=1\end{array} \right.\)
`n, (x+3)^2-(x+1)^3=56`
⇒ sai đề đó bạn ơi
`o, (x-4)(x-5)(x-6)(x-7)=1680`
⇒`(x^2-5x-4x+20)(x-6)(x-7)=1680`
⇒`(x^3-15x^2+74x-120)(x-7)=1680`
⇒`x^4-22x^3+179x^2-638x+840=1680`
⇒`x^4+x^3-13x^3-23x^2+202x^2+202x^2-840x-840=0`
⇒`x^3(x+1)-23x^2(x+1)+202x(x+1)-840(x+1)=0`
⇒`(x+1)(x^2(x-12)-11x(x-12)+70(x-12))=0`
⇒`(x+1)(x-12)(x^2-11x+70)=0`
⇒\(\left[ \begin{array}{l}x+1=0\\x-12=0\\x^2-11x+70=0\end{array} \right.\)
⇒`\(\left[ \begin{array}{l}x=-1\\x=12\\x∉RR\end{array} \right.\)
