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a) \(ĐKXĐ:\hept{\begin{cases}a\ne1\\a\ne0\end{cases}}\)
\(M=\left(\frac{\left(a-1\right)^2}{3a+\left(a-1\right)^2}-\frac{1-2a^2+4a}{a^3-1}+\frac{1}{a-1}\right)\div\frac{a^3+4a}{4a^2}\)
\(\Leftrightarrow M=\left(\frac{\left(a-1\right)^2}{a^2+a+1}-\frac{1-2a^2+4a}{\left(a-1\right)\left(a^2+a+1\right)}+\frac{1}{a-1}\right):\frac{a^2+4}{4a}\)
\(\Leftrightarrow M=\frac{\left(a-1\right)^3-1+2a^2-4a+a^2+a+1}{\left(a-1\right)\left(a^2+a+1\right)}\cdot\frac{4a}{a^2+4}\)
\(\Leftrightarrow M=\frac{a^3-3a^2+3a-1-1+2a^2-4a+a^2+a+1}{\left(a-1\right)\left(a^2+a+1\right)}\cdot\frac{4a}{a^2+4}\)
\(\Leftrightarrow M=\frac{a^3-1}{\left(a-1\right)\left(a^2+a+1\right)}\cdot\frac{4a^2}{a^2+4}\)
\(\Leftrightarrow M=\frac{4a^2}{a^2+4}\)
b) Ta có : \(\frac{4a^2}{a^2+4}=\frac{4\left(a^2+4\right)-16}{a^2+4}\)
\(=4-\frac{16}{a^2+4}\)
Để M đạt giá trị lớn nhất
\(\Leftrightarrow\frac{16}{a^2+4}\)min
\(\Leftrightarrow a^2+4\)max
\(\Leftrightarrow a\)max
Vậy để M đạt giá trị lớn nhất thì a phải đạ giá trị lớn nhất.
a) \(ĐKXĐ:\hept{\begin{cases}a\ne-3\\a\ne\pm2\end{cases}}\)
\(M=\frac{2a-a^2}{a+3}\left(\frac{a-2}{a+2}-\frac{a+2}{a-2}+\frac{4a^2}{4-a^2}\right)\)
\(\Leftrightarrow M=\frac{a\left(2-a\right)}{a+3}\cdot\frac{\left(a-2\right)^2-\left(a+2\right)^2-4a^2}{\left(a-2\right)\left(a+2\right)}\)
\(\Leftrightarrow M=\frac{a\left(2-a\right)}{a+3}\cdot\frac{a^2-4a+4-a^2-4a-4-4a^2}{\left(a-2\right)\left(a+2\right)}\)
\(\Leftrightarrow M=\frac{a\left(2-a\right)}{a+3}\cdot\frac{-4a^2-8a}{\left(a-2\right)\left(a+2\right)}\)
\(\Leftrightarrow M=\frac{a\left(2-a\right)}{a+3}\cdot\frac{-4a\left(a+2\right)}{\left(a-2\right)\left(a+2\right)}\)
\(\Leftrightarrow M=\frac{a\left(2-a\right)}{a+3}\cdot\frac{-4a}{a-2}\)
\(\Leftrightarrow M=\frac{4a^2\left(a-2\right)}{\left(a+3\right)\left(a-2\right)}\)
\(\Leftrightarrow M=\frac{4a^2}{a+3}\)
b) Để M = 1
\(\Leftrightarrow\frac{4a^2}{a+3}=1\)
\(\Leftrightarrow4a^2=a+3\)
\(\Leftrightarrow4a^2-a-3=0\)
\(\Leftrightarrow\left(4a+3\right)\left(a-1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}4a+3=0\\a-1=0\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}a=-\frac{3}{4}\left(tm\right)\\a=1\left(tm\right)\end{cases}}\)
Vậy để \(M=1\Leftrightarrow a\in\left\{-\frac{3}{4};1\right\}\)
c) Để M > 0
\(\Leftrightarrow\frac{4a^2}{a+3}>0\)
\(\Leftrightarrow a+3>0\)(Vì 4a2 > 0, loại trường hợp = 0)
\(\Leftrightarrow a>-3\)
Vậy để \(M>0\Leftrightarrow a>-3\)
Để M < 0
\(\Leftrightarrow\frac{4a^2}{a+3}< 0\)
\(\Leftrightarrow a+3< 0\)(Vì 4a2 > 0, loại trường hợp = 0)
\(\Leftrightarrow a< -3\)
Vậy để \(M< 0\Leftrightarrow a< -3\)
a) \(a\ne0;a\ne1\)
\(\Leftrightarrow M=\left[\frac{\left(a-1\right)^2}{3a+\left(a-1\right)^2}-\frac{1-2a^2+4a}{a^3-1}+\frac{1}{a-1}\right]:\frac{a^3+4a}{4a^2}\)
\(=\left[\frac{\left(a-1\right)^2}{a^2+a+1}-\frac{1-2a^2+4a}{\left(a-1\right)\left(a^2+a+1\right)}+\frac{1}{a-1}\right]\cdot\frac{4a^2}{a\left(a^2+4\right)}\)
\(=\frac{\left(a-1\right)^3-1+2a^2-4a+a^2+a+1}{\left(a-1\right)\left(a^2+a+1\right)}\cdot\frac{4a}{a^2+4}\)
\(=\frac{a^3-1}{a^3-1}\cdot\frac{4a}{a^2+4}=\frac{4a}{a^2+4}\)
Vậy \(M=\frac{4a}{a^2+4}\left(a\ne0;a\ne1\right)\)
b) \(M=\frac{4a}{a^2+4}\left(a\ne0;a\ne1\right)\)
M>0 khi 4a>0 => a>0
Kết hợp với ĐKXĐ
Vậy M>0 khi a>0 và a\(\ne\)1
c) \(M=\frac{4a}{a^2+4}\left(a\ne0;a\ne1\right)\)
\(M=\frac{4a}{a^2+4}=\frac{\left(a^2+4\right)-\left(a^2-4a+4\right)}{a^2+4}=1-\frac{\left(a-2\right)^2}{a^2+4}\)
Vì \(\frac{\left(a-2\right)^2}{a^2+4}\ge0\forall a\)nên \(1-\frac{\left(a-2\right)^2}{a^2+4}\le1\forall a\)
Dấu "=" <=> \(\frac{\left(a-2\right)^2}{a^2+4}=0\)\(\Leftrightarrow a=2\)
Vậy \(Max_M=1\)khi a=2
a) \(ĐK:a\ne1;a\ne0\)
\(A=\left[\frac{\left(a-1\right)^2}{3a+\left(a-1\right)^2}-\frac{1-2a^2+4a}{a^3-1}+\frac{1}{a-1}\right]:\frac{a^3+4a}{4a^2}=\left[\frac{a^2-2a+1}{a^2+a+1}-\frac{1-2a^2+4a}{a^3-1}+\frac{a^2+a+1}{a^3-1}\right].\frac{4a^2}{a^3+4a}\)\(=\left[\frac{a^3-3a^2+3a-1}{a^3-1}-\frac{1-2a^2+4a}{a^3-1}+\frac{a^2+a+1}{a^3-1}\right].\frac{4a^2}{a^3+4a}=\frac{a^3-1}{a^3-1}.\frac{4a}{a^2+4}=\frac{4a}{a^2+4}\)
b) Ta có: \(a^2+4\ge4a\)(*)
Thật vậy: (*)\(\Leftrightarrow\left(a-2\right)^2\ge0\)
Khi đó \(\frac{4a}{a^2+4}\le1\)
Vậy MaxA = 1 khi x = 2
