Giải bất phương trình:
\(\dfrac{1}{x-2}+\dfrac{1}{x-1}>\dfrac{1}{x}\)
giải bất phương trình: \(\sqrt{x+\dfrac{1}{x^2}}+\sqrt{x-\dfrac{1}{x^2}}>\dfrac{2}{x}\)
Giải bất phương trình:
\(\dfrac{1}{x^2}+\dfrac{x^2}{1-x^2}+\dfrac{5}{2}\left(\dfrac{\sqrt{1-x^2}}{x}+\dfrac{x}{\sqrt{1-x^2}}\right)+2>0\)
\(\dfrac{1}{x+2}+x-1< \dfrac{1}{x+1}+\sqrt{x^2+1}\)
giải bất phương trình
Giải bất phương trình :
a, \(\dfrac{x-1}{x-1-\sqrt{x^2-x}}\dfrac{>}{ }2x\)
b, \(\dfrac{1-\sqrt{1-8x^2}}{2x}< 1\)
Giải bất phương trình: \(\dfrac{x-2}{x+1}\)≥ \(\dfrac{3x+2}{x-1}-2\)
\(BPT\Leftrightarrow\dfrac{\left(x-2\right)\left(x-1\right)}{\left(x+1\right)\left(x-1\right)}\ge\dfrac{\left(3x+2\right)\left(x+1\right)}{\left(x+1\right)\left(x-1\right)}-\dfrac{2\left(x+1\right)\left(x-1\right)}{\left(x+1\right)\left(x-1\right)}\)
\(\Rightarrow x^2-x-2x+2-3x^2-3x-2x-2-2x^2-2\ge0\)
\(\Leftrightarrow-4x^2-8x-2\ge0\)
\(\Leftrightarrow x^2+2x+\dfrac{1}{2}\ge0\)
\(\Leftrightarrow\left(x+1\right)^2-\dfrac{1}{2}\ge0\)
Vậy bất phương trình luôn đúng \(\forall x\).
ĐKXĐ: \(x\ne1,-1\)
Ta có: \(\dfrac{x-2}{x+1}\ge\dfrac{3x+2}{x-1}-2\)
\(\dfrac{x-2}{x+1}\ge\dfrac{3x+2-2\left(x-1\right)}{x-1}\)
\(\dfrac{x-2}{x+1}-\dfrac{3x+2-2x+2}{x-1}\ge0\)
\(\dfrac{x-2}{x+1}-\dfrac{x+4}{x-1}\ge0\)
\(\dfrac{\left(x-2\right)\left(x-1\right)-\left(x-4\right)\left(x+1\right)}{x^2-1}\ge0\)
\(\dfrac{x^2-3x+2-x^2+3x+4}{x^2-1}\ge0\)
\(\dfrac{6}{x^2-1}\ge0\)
\(\Rightarrow x^2-1>0\Leftrightarrow x^2>1\Leftrightarrow\left\{{}\begin{matrix}x< -1\\x>1\end{matrix}\right.\)(TM)
Biểu thức vế trái có nghĩa khi
\(x\ne-2;x\ne1\\ \dfrac{x-2}{x+2}+\dfrac{x+1}{x-1}\Leftrightarrow\dfrac{x-2}{x+2}+\dfrac{x+1}{x-1}-2>0\\ \dfrac{\left(x-2\right)\left(x-1\right)+\left(x+2\right)\left(x+1\right)-2\left(x+2\right)\left(x-1\right)}{\left(x+2\right)\left(x-1\right)}\\ >0\\ \Leftrightarrow\dfrac{8-2x}{\left(x+2\right)\left(x-1\right)}>0\\ \Leftrightarrow\dfrac{4-x}{\left(x+2\right)\left(x-1\right)}>0\)
\(\Leftrightarrow\left(x+2\right)\left(x-1\right)\left(x-4\right)< 0\)
Lập bảng xét dấu
x | -2 | 1 | 4 |
x+2 | - 0 + | + | + |
x-1 | - - | 0 + | + |
x-4 | - - | - | 0 + |
VT | - 0 + | 0 - | 0 + |
Vậy nghiệm của bất pt là
\(x< -2.hay.1< x< 4\)
Giải bất phương trình:
\(\dfrac{15x-2}{4}\) - \(\dfrac{x^2+1}{3}\) > \(\dfrac{x\left(1-2x\right)}{6}\) + \(\dfrac{x-3}{2}\)
\(\dfrac{15x-2}{4}-\dfrac{x^2+1}{3}>\dfrac{x\left(1-2x\right)}{6}+\dfrac{x-3}{2}\\ \Leftrightarrow3\left(15x-2\right)-4\left(x^2+1\right)>2x\left(1-2x\right)+6\left(x-3\right)\\ \Leftrightarrow45x-6-4x^2-4>2x-4x^2+6x-18\\ \Leftrightarrow45x-6x-2x>6+4-18\\ \Leftrightarrow37x>-8\\ \Leftrightarrow x>-\dfrac{8}{37}\)
\(\dfrac{3\left(15x-2\right)}{12}-\dfrac{4\left(x^2+1\right)}{12}>\dfrac{2x\left(1-2x\right)}{12}+\dfrac{6\left(x-3\right)}{12}\)
\(45x-6-\left(4x^2+4\right)>2x-4x^2+6x-18\)
\(45x-4x^2+4x^2-2x-6x>6+4-18\)
\(37x>-8\)
\(x>\dfrac{-8}{37}\)
Giải các bất phương trình
a) \(x+2\le\sqrt[3]{x^3+8}\)
b)\(\sqrt{\dfrac{1}{x^2}-\dfrac{3}{4}}< \dfrac{1}{x}-\dfrac{1}{2}\)
Giải bất phương trình
\(\dfrac{\sqrt{x+1}}{\sqrt{x+1}-\sqrt{3-x}}>x-\dfrac{1}{2}\)
ĐKXĐ: \(\left\{{}\begin{matrix}-1\le x\le3\\x\ne1\end{matrix}\right.\)
\(\dfrac{\sqrt{x+1}\left(\sqrt{x+1}+\sqrt{3-x}\right)}{2\left(x-1\right)}>x-\dfrac{1}{2}\)
\(\Leftrightarrow\dfrac{x+1+\sqrt{-x^2+2x+3}}{x-1}>2x-1\)
- TH1: Với \(x>1\) BPT tương đương:
\(x+1+\sqrt{-x^2+2x+3}>\left(2x-1\right)\left(x-1\right)\)
\(\Leftrightarrow\sqrt{-x^2+2x+3}>2x^2-4x\)
Đặt \(\sqrt{-x^2+2x+3}=t\ge0\Rightarrow2x^2-4x=-2t^2+6\)
BPt trở thành: \(t>-2t^2+6\Leftrightarrow2t^2+t-6>0\)
\(\Rightarrow t>\dfrac{3}{2}\Rightarrow-x^2+2x+3>\dfrac{9}{4}\Rightarrow1< x< \dfrac{2+\sqrt{7}}{2}\)
TH2: với \(x< 1\) BPT tương đương:
\(x+1+\sqrt{-x^2+2x+3}< \left(2x-1\right)\left(x-1\right)\)
\(\Leftrightarrow\sqrt{-x^2+2x+3}< 2x^2-4x\)
Tương tự như trên, đặt \(t=\sqrt{-x^2+2x+3}\ge0\) ta được \(0\le t< \dfrac{3}{2}\)
\(\Rightarrow-x^2+2x+3< \dfrac{9}{4}\) \(\Rightarrow-1\le x< \dfrac{2-\sqrt{7}}{2}\)
Vậy nghiệm của BPT là: \(\left[{}\begin{matrix}-1\le x< \dfrac{2-\sqrt{7}}{2}\\1< x< \dfrac{2+\sqrt{7}}{2}\end{matrix}\right.\)
Giải bất phương trình
\(\dfrac{x^2+2x+2}{x+1}\ge\dfrac{x^2+4x+5}{x+1}-1\)
ĐKXĐ : x khác -1
\(\dfrac{x^2+2x+2}{x+1}\ge\dfrac{x^2+3x+4}{x+1}\\ \Leftrightarrow\dfrac{x^2+2x+2}{x+1}\ge\dfrac{x^2+2x+2}{x+1}+\dfrac{x+2}{x+1}\\ \Leftrightarrow\dfrac{x+2}{x+1}\le0\\ \Leftrightarrow x+2\ge0;x+1< 0\Leftrightarrow-1>x\ge-2\)