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\(x^6-14x^4+49x^2>36\)
\(\Leftrightarrow x^6-x^5+x^5-x^4-13x^4+13x^3-13x^3+13x^2+36x^2-36x+36x-36>0\)
\(\Leftrightarrow x^5\left(x-1\right)+x^4\left(x-1\right)-13x^3\left(x-1\right)-13x^2\left(x-1\right)+36x\left(x-1\right)+36\left(x-1\right)>0\)
\(\Leftrightarrow\left(x-1\right)\left(x^5+x^4-13x^3-13x^2+36x+36\right)>0\)
\(\Leftrightarrow\left(x-1\right)\left[x^4\left(x+1\right)-13x^2\left(x+1\right)+36\left(x+1\right)\right]>0\)
\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x^4-13x^2+36\right)>0\)
\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x^4-9x^2-4x^2+36\right)>0\)
\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left[x^2\left(x^2-9\right)-4\left(x^2-9\right)\right]>0\)
\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x^2-9\right)\left(x^2-4\right) >0\)
\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x-2\right)\left(x+2\right)\left(x+3\right)\left(x-3\right)>0\)
Để \(\left(x-1\right)\left(x+1\right)\left(x-2\right)\left(x+2\right)\left(x+3\right)\left(x-3\right)>0\)
\(\Rightarrow\left[{}\begin{matrix}x>3\\x< -3\end{matrix}\right.\)
Vậy để \(\left(x-1\right)\left(x+1\right)\left(x-2\right)\left(x+2\right)\left(x+3\right)\left(x-3\right)>0\) thì x>3 hoặc x<-3
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\(x^2\ge0\)
\(\Rightarrow\)\(x^2+2014\ge2014\)
\(\Rightarrow\)\(\left|x^2+2014\right|=x^2+2014\)
Vậy ta có: \(x^2+2014=1\)
\(\Leftrightarrow\) \(x^2=-2013\) vô lí
Vậy pt vô nghiệm
Vì x2+2014>0 với mọi x => \(|x^2+2014|=x^2+2014\ge2014\)
\(\Rightarrow\)Đẳng thức ở đề bài không thể xảy ra
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Ta có : \(\dfrac{3-7x}{1+x}\ge\dfrac{1}{2}\)
\(\Leftrightarrow\dfrac{3-7x}{1+x}-\dfrac{1}{2}\ge0\)
\(\Leftrightarrow\dfrac{2\left(3-7x\right)-\left(x+1\right)}{2\left(x+1\right)}\ge0\)
\(\Leftrightarrow\dfrac{5-15x}{2\left(x+1\right)}=\dfrac{5\left(3-x\right)}{2\left(x+1\right)}\ge0\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}3-x\ge0\\x+1>0\end{matrix}\right.\\\left\{{}\begin{matrix}3-x\le0\\x+1< 0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x\le3\\x>-1\end{matrix}\right.\\\left\{{}\begin{matrix}x\ge3\\x< -1\end{matrix}\right.\end{matrix}\right.\)
Vậy suy ra tập nghiệm
b, (x+4)(5x+9)-x>4
\(\Leftrightarrow\)5x2+29x+36-x>4
\(\Leftrightarrow\)5x2+28x+36>4
\(\Leftrightarrow\)5x2+28x+32>0
\(\Leftrightarrow\)5(x2+\(\dfrac{28}{5}\)x+\(\dfrac{32}{5}\))>0
\(\Leftrightarrow\)x2+\(\dfrac{28}{5}\)x+\(\dfrac{32}{5}\)>0
\(\Leftrightarrow\)x2+2.\(\dfrac{14}{5}\)x+\(\dfrac{206}{25}\)+\(\dfrac{32}{5}\)-\(\dfrac{206}{25}\)>0
\(\Leftrightarrow\)(x+\(\dfrac{14}{5}\))2-\(\dfrac{46}{25}\)>0
\(\Leftrightarrow\)(x+\(\dfrac{14-\sqrt{46}}{5}\))(x+\(\dfrac{14+\sqrt{46}}{5}\))>0
\(\Leftrightarrow\)2 trường hợp
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Tôi nghĩ là như này :)) Sai thì chịu nhá :((
Ta có pt : \(\left|x+1\right|+3\left|x-1\right|=x+2+\left|x\right|+2\left|x-2\right|\) (1)
Ta thấy VT pt (1) là : \(\left|x+1\right|+3\left|x-1\right|\ge0\forall x\)
Nên VP pt (1) cũng phải lớn hơn bằng 0
Có nghĩa là \(x+2\ge0\) \(\Leftrightarrow x\ge-2\)
Khi đó : \(\left\{{}\begin{matrix}\left|x+1\right|=-\left(x+1\right)\\3\left|x-1\right|=3\left(1-x\right)\\\left|x\right|=-x\\2\left|x-2\right|=2\left(2-x\right)\end{matrix}\right.\)
Vậy pt (1) \(\Leftrightarrow-x-1+3-3x=x+2-x+4-2x\)
\(\Leftrightarrow2x=-4\Leftrightarrow x=-2\) ( thỏa mãn )
Vậy \(x=-2\) thỏa mãn pt.
\(\left|x+1\right|\) | - | + | + | + | + |
3\(\left|x-1\right|\) | - | - | + | + | + |
\(\left|x\right|\) | - | - | - | + | + |
\(2\left|x-2\right|\) | - | - | - | - | + |
PT | 2x-4=5x-2 | 2x-4=5x-2 | -4x+2=2x-2 | -4x+2=-2x+6 |
-1 0 1 2
1) x=-2/3>-1( loại)
2)
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Ta có : x2-2x+3|x-1| < 3
- Nếu x\(\ge\)1 thì có : x2 -2x+3(x-1) < 3 \(\Leftrightarrow\)x2-x-3<3 \(\Leftrightarrow\)x2-x-6<0 \(\Leftrightarrow\)(x-3)(x+2)<0\(\Leftrightarrow\)x<3 hoặc x<-2 =>x<-2
- Nếu x<1 thì ta có :
- Nếu 1<0 thì ta có : x2-2x+3(1-x) < 3 \(\Leftrightarrow\)x2-5x+3 < 3\(\Leftrightarrow\)x2-5x < 0 \(\Leftrightarrow\)x(x-5) < 0\(\Rightarrow\)x< 0 hoặc x< 5