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\(M=\left(\frac{a-2\sqrt{a}+1}{a+1}\right):\left[\frac{1}{\sqrt{a}-1}-\frac{2\sqrt{a}}{\sqrt{a}\left(a+1\right)-\left(a+1\right)}\right]\)
\(M=\left[\frac{\left(\sqrt{a}-1\right)^2}{a+1}\right]:\left[\frac{1}{\sqrt{a}-1}-\frac{2\sqrt{a}}{\left(a+1\right)\left(\sqrt{a}-1\right)}\right]\)
\(M=\frac{\left(\sqrt{a}-1\right)^2}{a+1}:\left[\frac{a+1-2\sqrt{a}}{\left(\sqrt{a}-1\right)\left(a+1\right)}\right]\)
\(M=\frac{\left(\sqrt{a}-1\right)^2}{a+1}:\frac{\left(\sqrt{a}-1\right)^2}{\left(\sqrt{a}-1\right)\left(a+1\right)}\)
\(M=\frac{\left(\sqrt{a}-1\right)^2}{a+1}.\frac{\left(\sqrt{a}-1\right)\left(a+1\right)}{\left(\sqrt{a}-1\right)^2}=\sqrt{a}+1\)
\(M>1\Leftrightarrow\sqrt{a}-1>1\Leftrightarrow\sqrt{a}>2\Leftrightarrow a>4\)
\(M=\sqrt{3-2\sqrt{2}}-1\)
\(M=\sqrt{\left(\sqrt{2}-1\right)^2}-1=\sqrt{2}-1-1=\sqrt{2}-2\)
chỉ làm được câu a do hơi gà
\(P=\frac{1}{2\left(1+\sqrt{a}\right)}+\frac{1}{2\left(1-\sqrt{a}\right)}-\frac{a^2+2}{1-a^3}\)
\(=\frac{1-\sqrt{a}+1+\sqrt{a}}{2\left(1-a\right)}-\frac{a^2+2}{\left(1-a\right)\left(1-a+a^2\right)}\)
\(=\frac{1-a+a^2-a^2+2}{\left(1-a\right)\left(1-a+a^2\right)}=\frac{3-a}{\left(1-a\right)\left(1-a+a^2\right)}\)
sửa dòng cuối :))
\(\frac{1-a+a^2-a^2-2}{\left(1-a\right)\left(1-a+a^2\right)}=\frac{-1-a}{\left(1-a\right)\left(1-a+a^2\right)}\)
a) \(A=\left(\frac{1}{a-\sqrt{a}}+\frac{1}{\sqrt{a}-1}\right):\frac{\sqrt{a}+1}{a-2\sqrt{a}+1}\left(a>0;a\ne1\right)\)
\(=\left[\frac{1}{\sqrt{a}\left(\sqrt{a}-1\right)}+\frac{1}{\sqrt{a}-1}\right]:\frac{\sqrt{a}+1}{\left(\sqrt{a}-1\right)^2}\)
\(=\frac{1+\sqrt{a}}{\sqrt{a}\left(\sqrt{a}-1\right)}\cdot\frac{\left(\sqrt{a}-1\right)^2}{\sqrt{a}+1}\)
\(=\frac{\sqrt{a}-1}{\sqrt{a}}\)
b) Để \(A=\frac{1}{2}\)
\(\Leftrightarrow\frac{\sqrt{a}-1}{\sqrt{a}}=\frac{1}{2}\)
\(\Leftrightarrow2\sqrt{a}-2=\sqrt{a}\)
\(\Leftrightarrow\sqrt{a}=2\Leftrightarrow a=4\left(tm\right)\)
\(A=\frac{\sqrt{a}}{1+\sqrt{a}}+\frac{3-\sqrt{a}}{a-1}\)
ĐKXĐ : \(\hept{\begin{cases}a\ge0\\a\ne1\end{cases}}\)
a) \(=\frac{\sqrt{a}}{\sqrt{a}+1}+\frac{3-\sqrt{a}}{\left(\sqrt{a}-1\right)\left(\sqrt{a}+1\right)}\)
\(=\frac{\sqrt{a}\left(\sqrt{a}-1\right)}{\left(\sqrt{a}-1\right)\left(\sqrt{a}+1\right)}+\frac{3-\sqrt{a}}{\left(\sqrt{a}-1\right)\left(\sqrt{a}+1\right)}\)
\(=\frac{a-\sqrt{a}+3-\sqrt{a}}{\left(\sqrt{a}-1\right)\left(\sqrt{a}+1\right)}\)
\(=\frac{a-2\sqrt{a}+3}{\left(\sqrt{a}-1\right)\left(\sqrt{a}+1\right)}\)
b) Để A = -2
=> \(\frac{a-2\sqrt{a}+3}{\left(\sqrt{a}-1\right)\left(\sqrt{a}+1\right)}=-2\)( ĐKXĐ : \(\hept{\begin{cases}a\ge0\\a\ne1\end{cases}}\))
=> \(a-2\sqrt{a}+3=-2\left(a-1\right)\)
=> \(a-2\sqrt{a}+3=-2a+2\)
=> \(a+2a+3-2=2\sqrt{a}\)
=> \(3a+1=2\sqrt{a}\)
Bình phương hai vế
=> \(9a^2+6a+1=4a\)
=> \(9a^2+6a+1-4a=0\)
=> \(9a^2+2a+1=0\)
Ta có : \(9a^2+2a+1=9\left(a^2+\frac{2}{9}a+\frac{1}{81}\right)+\frac{8}{9}=9\left(a+\frac{1}{9}\right)^2+\frac{8}{9}\ge\frac{8}{9}>0\forall a\)
=> phương trình vô nghiệm
\(P=\left(\frac{1}{\sqrt{a}-1}-\frac{1}{\sqrt{a}}\right):\left(\frac{\sqrt{a}+1}{\sqrt{a}-2}-\frac{\sqrt{a}+2}{\sqrt{a}-1}\right)\)
\(=\frac{\sqrt{a}-\sqrt{a}+1}{\sqrt{a}\cdot\left(\sqrt{a}-1\right)}:\frac{\left(\sqrt{a}+1\right)\left(\sqrt{a}-1\right)-\left(\sqrt{a}+2\right)\left(\sqrt{a}-2\right)}{\left(\sqrt{a}-1\right)\left(\sqrt{a}-2\right)}\)
\(=\frac{1}{\sqrt{a}\left(\sqrt{a}-1\right)}\cdot\frac{\left(\sqrt{a}-1\right)\left(\sqrt{a}-2\right)}{a-1-a+4}\)
\(=\frac{\sqrt{a}-2}{3\sqrt{a}}\)
\(A=\left(\frac{a+\sqrt{a}}{\sqrt{a}+1}+1\right).\)\(\left(\frac{a-\sqrt{a}}{\sqrt{a}-1}-1\right)\)
\(=\left(\frac{\sqrt{a}\left(\sqrt{a}+1\right)}{\sqrt{a}+1}+1\right)\)\(\left(\frac{-\sqrt{a}\left(\sqrt{a}-1\right)}{\sqrt{a}-1}-1\right)\)
\(=\left(\sqrt{a}+1\right)\left(-\sqrt{a}-1\right)\)
\(=-\left(\sqrt{a}+1\right)\left(\sqrt{a}+1\right)=-\left(\sqrt{a}+1\right)^2\)
\(b,A=-a^2\Rightarrow-\left(\sqrt{a}+1\right)^2=a^2\)
\(\Leftrightarrow a=\sqrt{a}+1\Rightarrow a-\sqrt{a}-1=0\)
\(\Rightarrow4a-4\sqrt{a}-4=0\)
\(\Rightarrow4a-4\sqrt{a}+1-5=0\)
\(\Rightarrow\left(2\sqrt{a}-1\right)^2-\sqrt{5}^2=0\)
\(\Rightarrow\left(2\sqrt{a}-1+\sqrt{5}\right)\left(2\sqrt{a}-1-\sqrt{5}\right)=0\)
\(\Rightarrow\orbr{\begin{cases}2\sqrt{a}=1-\sqrt{5}\\2\sqrt{a}=1+\sqrt{5}\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}\sqrt{a}=\frac{1-\sqrt{5}}{2}\\\sqrt{a}=\frac{1+\sqrt{5}}{2}\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}a=\frac{\left(1-\sqrt{5}\right)^2}{4}\left(tm\right)\\a=\frac{\left(1+\sqrt{5}\right)^2}{4}\left(tm\right)\end{cases}}\)