Câu hỏi của Dương Lee

Question

Cho A= x(x-$\dfrac{1}{2}$).Tìm x đểa,A=0     b,A<0     c,A>0

2611 · Accepted Answer

`a)A=0``=>x(x-1/2)=0``@TH1:x=0``@TH2:x-1/2=0=>x=1/2`_______________________________________`b)A < 0``=>x(x-1/2) < 0``@TH1:{(x < 0),(x-1/2 > 0):}=>{(x < 0),(x > 1/2):}=>x` không có giá trị t/m`@TH2:{(x > 0),(x-1/2 < 0):}=>{(x > 0),(x < 1/2):}=>0 < x < 1/2`_____________________________________________`c)A > 0``=>x(x-1/2) > 0``@TH1:{(x > 0),(x-1/2 > 0):}=>{(x > 0),(x > 1/2):}=>x > 1/2``@TH2:{(x < 0),(x-1/2 < 0):}=>{(x < 0),(x < 1/2):}=>x < 0`Câu trả lời: `a)A=0``=>x(x-1/2)=0``@TH1:x=0``@TH2:x-1/2=0=>x=1/2`_______________________________________`b)A < 0``=>x(x-1/2) < 0``@TH1:{(x < 0),(x-1/2 > 0):}=>{(x < 0),(x > 1/2):}=>x` không có giá trị t/m`@TH2:{(x > 0),(x-1/2 < 0):}=>{(x > 0),(x < 1/2):}=>0 < x < 1/2`_____________________________________________`c)A > 0``=>x(x-1/2) > 0``@TH1:{(x > 0),(x-1/2 > 0):}=>{(x > 0),(x > 1/2):}=>x > 1/2``@TH2:{(x < 0),(x-1/2 < 0):}=>{(x < 0),(x < 1/2):}=>x < 0`

Vui lòng để tên hiển thị · Answer

`a, A = 0 => x(x-1/2) = 0``=>` $\left[{}\begin{matrix}x=0\x-\dfrac{1}{2}=0\end{matrix}\right.$`=>` $\left[{}\begin{matrix}x=0\x=\dfrac{1}{2}\end{matrix}\right.$`b, A < 0``=>` $\left[{}\begin{matrix}\left[{}\begin{matrix}x>0\x-\dfrac{1}{2}< 0\end{matrix}\right.\\left[{}\begin{matrix}x< 0\x-\dfrac{1}{2}>0\end{matrix}\right.\end{matrix}\right.$`->` $\left[{}\begin{matrix}\left[{}\begin{matrix}x>0\x< \dfrac{1}{2}\end{matrix}\right.\\left[{}\begin{matrix}x< 0\x>\dfrac{1}{2}\end{matrix}\right.\end{matrix}\right.$`=>` x < 1/2``c, A > 0``=>` $\left[{}\begin{matrix}\left[{}\begin{matrix}x>0\x-\dfrac{1}{2}>0\end{matrix}\right.\\left[{}\begin{matrix}x< 0\x-\dfrac{1}{2}< 0\end{matrix}\right.\end{matrix}\right.$`=>` $\left[{}\begin{matrix}\left[{}\begin{matrix}x>0\x>\dfrac{1}{2}\end{matrix}\right.\\left[{}\begin{matrix}x< 0\x< \dfrac{1}{2}\end{matrix}\right.\end{matrix}\right.$`=> x > 1/2` hoặc `x < 0`Câu trả lời: `a, A = 0 => x(x-1/2) = 0``=>` $\left[{}\begin{matrix}x=0\x-\dfrac{1}{2}=0\end{matrix}\right.$`=>` $\left[{}\begin{matrix}x=0\x=\dfrac{1}{2}\end{matrix}\right.$`b, A < 0``=>` $\left[{}\begin{matrix}\left[{}\begin{matrix}x>0\x-\dfrac{1}{2}< 0\end{matrix}\right.\\left[{}\begin{matrix}x< 0\x-\dfrac{1}{2}>0\end{matrix}\right.\end{matrix}\right.$`->` $\left[{}\begin{matrix}\left[{}\begin{matrix}x>0\x< \dfrac{1}{2}\end{matrix}\right.\\left[{}\begin{matrix}x< 0\x>\dfrac{1}{2}\end{matrix}\right.\end{matrix}\right.$`=>` x < 1/2``c, A > 0``=>` $\left[{}\begin{matrix}\left[{}\begin{matrix}x>0\x-\dfrac{1}{2}>0\end{matrix}\right.\\left[{}\begin{matrix}x< 0\x-\dfrac{1}{2}< 0\end{matrix}\right.\end{matrix}\right.$`=>` $\left[{}\begin{matrix}\left[{}\begin{matrix}x>0\x>\dfrac{1}{2}\end{matrix}\right.\\left[{}\begin{matrix}x< 0\x< \dfrac{1}{2}\end{matrix}\right.\end{matrix}\right.$`=> x > 1/2` hoặc `x < 0`

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