(x+3).(4-x)=7
⇒(x+3).(4-x)=7.1=1.7
TH1:Nếu x+3=7
⇒x=7-3=4 (1)
Nếu 4-x=1
x=4-1=3 (2)
Từ (1) và (2) suy ra xϵ∅
TH2:Nếu x+3=1
x=1-3=-2 (3)
Nếu 4-x=7
x=4-7=-3 (4)
Từ (3) và (4) suy ra xϵ∅
Từ trường hợp 1 và 2 suy ra xϵ∅
Vậy xϵ∅
Nhớ tck cho mình nha!!!!!!
\(\left(x+3\right)\left(4-x\right)=7.\)
\(\Rightarrow\left(x+3\right);\left(4-x\right)\in U_{\left(7\right)}=\left\{\pm1;\pm7\right\}.\)
Xét các trường hợp:
TH1: \(\left\{{}\begin{matrix}x+3=1\\4-x=7\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-2\\x=-3\end{matrix}\right.\left(tm\right).\)
TH2: \(\left\{{}\begin{matrix}x+3=7\\4-x=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=4\\x=3\end{matrix}\right.\left(tm\right).\)
TH3: \(\left\{{}\begin{matrix}x+3=-1\\4-x=-7\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-4\\x=11\end{matrix}\right.\left(tm\right).\)
TH4: \(\left\{{}\begin{matrix}x+3=-7\\4-x=-1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-10\\x=5\end{matrix}\right.\left(tm\right).\)
Vậy..........
\(\left(x+3\right)\cdot\left(4-x\right)=7\)
\(\Rightarrow\left(x+3\right)\cdot\left(4-x\right)=1\cdot7=7\cdot1=\left(-1\right)\cdot\left(-7\right)=\left(-7\right)\cdot\left(-1\right)\)
TH1: \(\left(x+3\right)\cdot\left(4-x\right)=1\cdot7\)
\(\Rightarrow x+3=1\Rightarrow x=\left(-2\right)\)
\(\Rightarrow4-x=7\Rightarrow x=\left(-3\right)\) (1)
TH2 : \(\left(x+3\right)\cdot\left(4-x\right)=7\cdot1\)
\(\Rightarrow x+3=7\Rightarrow x=4\)
\(\Rightarrow4-x=1\Rightarrow x=3\) (2)
TH3 : \(\left(x+3\right)\cdot\left(4-x\right)=\left(-1\right)\cdot\left(-7\right)\)
\(\Rightarrow x+3=\left(-1\right)\Rightarrow x=\left(-4\right)\)
\(\Rightarrow4-x=\left(-7\right)\Rightarrow x=11\) (3)
TH4 : \(\left(x+3\right)\cdot\left(4-x\right)=\left(-7\right)\cdot\left(-1\right)\)
\(\Rightarrow x+3=\left(-7\right)\Rightarrow x=\left(-10\right)\)
\(\Rightarrow4-x=\left(-1\right)\Rightarrow x=5\) (4)
Từ (1),(2),(3),(4) => x ϵ ∅
