Toán Lớp 8: Tìm x , biết :
1. (x-1)(x+1) = 3
2. x(x – 4) – 8 + 2x = 0
3.2x^2 – 3x = 2
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Toán Lớp 8: Tìm x , biết :
1. (x-1)(x+1) = 3
2. x(x – 4) – 8 + 2x = 0
3.2x^2 – 3x = 2
Comments ( 2 )
1. (x+1)(x-1)=3
=> x^2 -1=3
=> x^2 =3+1=4
=> x=±2
2. x(x – 4) – 8 + 2x = 0
=> x(x-4)-2(x-4)=0
=> (x-2)(x-4)=0
=> \(\left[ \begin{array}{l}x-2=0\\x-4=0\end{array} \right.\)
=> \(\left[ \begin{array}{l}x=2\\x=4\end{array} \right.\)
3. 2x^2 -3x=2
=> 2x^2 -3x-2=0
=> 2x^2 -4x+x-2=0
=> 2x(x-2)+(x-2)=0
=> (2x+1)(x-2)=0
=> \(\left[ \begin{array}{l}2x+1=0\\x-2=0\end{array} \right.\)
=> \(\left[ \begin{array}{l}2x=-1\\x=2\end{array} \right.\)
=> \(\left[ \begin{array}{l}x=-\frac{1}{2}\\x=2\end{array} \right.\)
Giải đáp + Lời giải và giải thích chi tiết:
1)\ (x-1)(x+1)=3
<=>x^{2}-1^{2}=3
<=>x^{2}=3+1=4=(+-2)^{2}
<=>x=+-2
2)\ x(x-4)-8+2x=0
<=>x(x-4)+2(x-4)=0
<=>(x-4)(x+2)=0
=> \(\left[ \begin{array}{l}x-4=0\\x+2=0\end{array} \right.\)
<=> \(\left[ \begin{array}{l}x=4\\x=-2\end{array} \right.\)
3)\ 2x^{2}-3x=2
<=>2x^{2}-3x-2=0
<=>(2x^{2}-4x)+(x-2)=0
<=>2x(x-2)+(x-2)=0
<=>(x-2)(2x+1)=0
=> \(\left[ \begin{array}{l}x-2=0\\2x+1=0\end{array} \right.\)
<=> \(\left[ \begin{array}{l}x=2\\x=-\dfrac{1}{2}\end{array} \right.\)