Toán Lớp 8: 1)x^2+6x+5=0
2)x^2-14x+13=0
3)x^2+8x+7=0
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Toán Lớp 8: 1)x^2+6x+5=0
2)x^2-14x+13=0
3)x^2+8x+7=0
Mọi người giúp mình với mik đang cần gấp lắm!
Comments ( 2 )
$\text{C1) }$$x^{2}+6x+5=0$
⇒$\text{}$$x^{2}+x+5x+5=0$
⇒$\text{(}$$x^{2}+x)+(5x+5)=0$
⇒$\text{x.(x+1)+5.(x+1)=0}$
⇒$\text{(x+1).(x+5)=0}$
⇒\(\left[ \begin{array}{l}x+1=0\\x+5=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=-1\\x=-5\end{array} \right.\)
$\text{C2) }$$x^{2}-14x+13=0$
⇒$\text{}$$x^{2}-x-13x+13=0$
⇒$\text{(}$$x^{2}-x)-(13x-13)=0$
⇒$\text{x.(x-1)-13.(x-1)=0}$
⇒$\text{(x-1).(x-13)=0}$
⇒\(\left[ \begin{array}{l}x-1=0\\x-13=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=1\\x=13\end{array} \right.\)
$\text{C3) }$$x^{2}+8x+7=0$
⇒$\text{}$$x^{2}+x+7x+7=0$
⇒$\text{(}$$x^{2}+x)+(7x+7)=0$
⇒$\text{x.(x+1)+7.(x+1)}=0$
⇒\text{(x+1).(x+7)=0}
⇒\(\left[ \begin{array}{l}x+1=0\\x+7=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=-1\\x=-7\end{array} \right.\)
\text{*Cách làm chung:}
\text{-Áp dụng phương pháp:}
\text{+Thêm bớt hạng tử}
\text{+Nhóm hạng tử}
\text{+Đặt nhân tử chung}
___________________________________
\text{#code}
Giải đáp:
$1) x^2+6x+5=0$
$⇔ x²+x+5x+5=0$
$⇔ x.(x+1)+5.(x+1)=0$
$⇔ (x+5).(x+1)=0$
$⇔$ \(\left[ \begin{array}{l}x+5=0\\x+1=0\end{array} \right.\)$⇔$ \(\left[ \begin{array}{l}x=-5\\x=-1\end{array} \right.\)
$\text{Vậy x ∈ {-5;-1}}$
$2) x^2-14x+13=0$
$⇔ x²-x-13x+13=0$
$⇔ x.(x-1)-13.(x-1)=0$
$⇔ (x-13).(x-1)=0$
$⇔$ \(\left[ \begin{array}{l}x-13=0\\x-1=0\end{array} \right.\)$⇔$ \(\left[ \begin{array}{l}x=13\\x=1\end{array} \right.\)
$\text{Vậy x ∈ {13;1}}$
$3) x^2+8x+7=0$
$⇔ x²+x+7x+7=0$
$⇔ x.(x+1)+7.(x+1)=0$
$⇔ (x+7).(x+1)=0$
$⇔$ \(\left[ \begin{array}{l}x+7=0\\x+1=0\end{array} \right.\) $⇔$ \(\left[ \begin{array}{l}x=-7\\x=-1\end{array} \right.\)
$\text{Vậy x ∈ {-7;-1}}$