Toán Lớp 8: a,2(x+3)=x² +3x
b, x ² +5x+6=0
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Toán Lớp 8: a,2(x+3)=x² +3x
b, x ² +5x+6=0
Comments ( 2 )
a, 2(x+3)=x^2+3x
=> 2(x+3)-x(x+3)=0
=> (x+3)(2-x)=0
=> $\left[\begin{matrix} x+3=0\\ 2-x=0\end{matrix}\right.$
=> $\left[\begin{matrix} x=-3\\ x=2\end{matrix}\right.$
Vậy x∈{-3 ; 2}
b, x^2+5x+6=0
=> x^2+2x+3x+6=0
=> x(x+2)+3(x+2)=0
=> (x+2)(x+3)=0
=> $\left[\begin{matrix} x+2=0\\ x+3=0\end{matrix}\right.$
=> $\left[\begin{matrix} x=-2\\ x=-3\end{matrix}\right.$
Vậy x∈{-3 ; -2}
Giải đáp:
a, 2.(x + 3) = x^2 + 3x
↔ 2.(x + 3) – x^2 – 3x = 0
↔ 2.(x + 3) – x.(x + 3) = 0
↔ (x + 3).(2 – x) = 0
↔ $\left[\begin{matrix} x+ 3 = 0\\ 2 – x = 0\end{matrix}\right.$
↔ $\left[\begin{matrix} x = -3\\ x = 2\end{matrix}\right.$
Vậy x ∈ {-3;2}
————————
b, x^2 + 5x + 6 = 0
↔ x^2 + 2x + 3x + 6 = 0
↔ x.(x + 2) + 3.(x + 2) = 0
↔ (x + 2).(x + 3) = 0
↔ $\left[\begin{matrix} x+ 3 = 0\\ x + 2 = 0\end{matrix}\right.$
↔ $\left[\begin{matrix} x = -3\\ x = -2\end{matrix}\right.$
Vậy x ∈ {-3; -2}
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