Toán Lớp 8: x ² +5x+6=0
(x-2) ²-(x-3)(x+3)=6
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Toán Lớp 8: x ² +5x+6=0
(x-2) ²-(x-3)(x+3)=6
Comments ( 2 )
x^2+5x+6=0
->x^2+2x+3x+6=0
->(x^2+2x)+(3x+6)=0
->x.(x+2)+3.(x+2)=0
->(x+2).(x+3)=0
->\(\left[ \begin{array}{l}x+2=0\\x+3=0\end{array} \right.\)
->\(\left[ \begin{array}{l}x=-2\\x=-3\end{array} \right.\)
Vậy x in {-2; -3}
$\\$
(x-2)^2-(x-3).(x+3)=6
->x^2-2.x.2+2^2-(x^2-3^2)=6
->x^2-4x+4-x^2+9=6
->(x^2-x^2)-4x+(4+9)=6
->-4x+13=6
->-4x=6-13
->-4x=-7
->x=(-7):(-4)
->x=\frac{7}{4}
Vậy x=\frac{7}{4}
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