Question

tìm x 

a, (x-8)*(x+30)>0

Answer 1

a)\(\left(x-8\right)\left(x+30\right)>0\)

\(\Leftrightarrow\begin{cases}x-8>0\\x+30>0\end{cases}\) hoặc \(\begin{cases}x-8< 0\\x+30< 0\end{cases}\)

\(\Leftrightarrow\begin{cases}x>8\\x>-30\end{cases}\) hoặc \(\begin{cases}x< 8\\x< -30\end{cases}\)

\(\Leftrightarrow x>8\) hoặc \(x< -30\)

Answer 2

(x - 8)(x+30)>0

(+) Với x - 8 ; x+30 cùng dương

\(\Rightarrow\begin{cases}x-8>0\\x+30>0\end{cases}\)

\(\Rightarrow\begin{cases}x>8\\x>-30\end{cases}\)

=> x > 8

(+) Với x - 8 ; x+30 cùng âm

\(\Rightarrow\begin{cases}x-8< 0\\x+30< 0\end{cases}\)

\(\Rightarrow\begin{cases}x< 8\\x< -30\end{cases}\)

=> x< - 30

Vậy x< -30 ; x>8

Answer 3

Ta có : \(\left(x-8\right)\left(x+30\right)>0\)

\(\Leftrightarrow\begin{cases}x-8>0\\x+30>0\end{cases}\) hoặc \(\begin{cases}x-8< 0\\x+30< 0\end{cases}\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x>8\\x< -30\end{array}\right.\)

Answer 4

\(\left(x-8\right)\left(x+30\right)>0\)
\(TH1:\Leftrightarrow\left[\begin{array}{nghiempt}x-8>0\\x+30>0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x>8\\x>-30\end{array}\right.\)\(\Rightarrow x>8\)
\(TH2:\Leftrightarrow\left[\begin{array}{nghiempt}x-8< 0\\x+30< 0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x< 8\\x< -30\end{array}\right.\)\(\Rightarrow x< -30\)
Vậy x>8 và x<-30

Answer 5

\(\left(x-8\right).\left(x+30\right)>0\)

\(TH1:\begin{cases}x-8>0\\x+30>0\end{cases}\)

\(\Rightarrow\begin{cases}x>8\\x>-30\end{cases}\Rightarrow x>8\)

\(TH2:\begin{cases}x-8< 0\\x+30< 0\end{cases}\)

\(\Rightarrow\begin{cases}x< 8\\x< -30\end{cases}\)

\(\Rightarrow x< -30\)

Vậy để \(\left(x-8\right).\left(x+30\right)>0\) thì \(x>8\) hoặc \(x>-30\)​