a) đkxđ \(x\ge-1\)

pt đã cho tương đương với

\(x^2-x=2\left(\sqrt{x+1}-\sqrt{x^3+1}\right)\)

\(\Leftrightarrow x^2-x=2.\dfrac{x+1-\left(x^3+1\right)}{\sqrt{x+1}+\sqrt{x^3+1}}\)

\(\Leftrightarrow x\left(x-1\right)=2.\dfrac{x\left(1-x\right)}{\sqrt{x+1}+\sqrt{x^3+1}}\)

\(\Leftrightarrow x\left(x-1\right)\left[1+\dfrac{1}{\sqrt{x+1}+\sqrt{x^3+1}}\right]=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\left(nhận\right)\\x=1\left(nhận\right)\\1+\dfrac{1}{\sqrt{x+1}+\sqrt{x^3+1}}=0\left(vôlí\right)\end{matrix}\right.\)

Vậy pt đã cho có tâp nghiệm \(S=\left\{0;-1\right\}\)

\(x^2-x+2\sqrt[]{x^3+1}=2\sqrt[]{x+1}\) 

\(\Leftrightarrow2\sqrt[]{x^3+1}-2\sqrt[]{x+1}-\left(x^2+x+\dfrac{1}{4}\right)+\dfrac{1}{4}=0\)

\(\Leftrightarrow2\sqrt[]{x+1}\left(\sqrt[]{x^2-x+1}-1\right)-\left(x^2+x+\dfrac{1}{4}\right)+\dfrac{1}{4}=0\)

\(\Leftrightarrow\left(x+\dfrac{1}{2}\right)^2=2\sqrt[]{x+1}\left(\sqrt[]{x^2-x+1}-1\right)-\dfrac{1}{4}\left(1\right)\)

mà \(\left(x+\dfrac{1}{2}\right)^2\ge0,\forall x\inℝ\)

\(\left(1\right)\Leftrightarrow2\sqrt[]{x+1}\left(\sqrt[]{x^2-x+1}-1\right)-\dfrac{1}{4}\ge0\)

\(\Leftrightarrow\sqrt[]{x+1}\left(\sqrt[]{x^2-x+1}-1\right)\ge\dfrac{1}{8}\left(2\right)\)

Điều kiện xác định :

\(\left\{{}\begin{matrix}x+1\ge0\\\sqrt[]{x^2-x+1}-1\ge0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x\ge-1\\\sqrt[]{x^2-x+1}\ge1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ge-1\\x^2-x+1\ge1\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x\ge-1\\x\left(x-1\right)\ge0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ge-1\\x\le0\cup x\ge1\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x\ge1\\-1\le x\le0\end{matrix}\right.\)

BPT \(\left(2\right)\Leftrightarrow\left(x+1\right)\left(x^2-x+1-2\sqrt[]{x^2-x+1}-1\right)\ge\dfrac{1}{64}\)

\(\Leftrightarrow\left(x^2-x-2\sqrt[]{x^2-x+1}\right)\ge\dfrac{1}{64}\left(vì.x+1\ge0\right)\)

Đặt \(t=\sqrt[]{x^2-x+1}>0\)

\(BPT\Leftrightarrow t^2-2t-1-\dfrac{1}{64}\ge0\)

\(\Leftrightarrow t^2-2t-\dfrac{63}{64}\ge0\)

\(\Leftrightarrow t^2-2t+1-1-\dfrac{63}{64}\ge0\)

\(\Leftrightarrow\left(t-1\right)^2-\dfrac{127}{64}\ge0\)

\(\Leftrightarrow\left(t-1-\dfrac{\sqrt[]{127}}{8}\right)\left(t-1+\dfrac{\sqrt[]{127}}{8}\right)\ge0\)

\(\Leftrightarrow\left[{}\begin{matrix}t\ge1+\dfrac{\sqrt[]{127}}{8}\\t\le1-\dfrac{\sqrt[]{127}}{8}\end{matrix}\right.\)

\(\Leftrightarrow t\ge1+\dfrac{\sqrt[]{127}}{8}\)  \(\left(t>0;1-\dfrac{\sqrt[]{127}}{8}< 0\right)\)

\(\Leftrightarrow\sqrt[]{x^2-x+1}\ge1+\dfrac{\sqrt[]{127}}{8}\)

\(\Leftrightarrow x^2-x+1\ge\left(1+\dfrac{\sqrt[]{127}}{8}\right)^2\)

mà \(x^2-x+1=\left(x-\dfrac{1}{2}\right)^2+\dfrac{3}{4}\ge\dfrac{3}{4},\forall x\)

      \(\dfrac{3}{4}< \left(1+\dfrac{\sqrt[]{127}}{8}\right)^2\)

\(\Leftrightarrow\left(x-\dfrac{1}{2}\right)^2\ge\left(1+\dfrac{\sqrt[]{127}}{8}\right)^2-\dfrac{3}{4}\)

\(\Leftrightarrow\left(x-\dfrac{1}{2}\right)^2\ge\left(1+\dfrac{\sqrt[]{127}}{8}\right)^2-\dfrac{3}{4}\)

\(\Leftrightarrow\left[{}\begin{matrix}x-\dfrac{1}{2}\le-\sqrt[]{\left(1+\dfrac{\sqrt[]{127}}{8}\right)^2-\dfrac{3}{4}}\\x-\dfrac{1}{2}\ge\sqrt[]{\left(1+\dfrac{\sqrt[]{127}}{8}\right)^2-\dfrac{3}{4}}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x\le-\sqrt[]{\left(1+\dfrac{\sqrt[]{127}}{8}\right)^2-\dfrac{3}{4}}+\dfrac{1}{2}\\x\ge\sqrt[]{\left(1+\dfrac{\sqrt[]{127}}{8}\right)^2-\dfrac{3}{4}}+\dfrac{1}{2}\end{matrix}\right.\)

\(\Leftrightarrow x\ge\sqrt[]{\left(1+\dfrac{\sqrt[]{127}}{8}\right)^2-\dfrac{3}{4}}+\dfrac{1}{2}\) (so với đkxđ \(\left[{}\begin{matrix}x\ge1\\-1\le x\le0\end{matrix}\right.\))

\(\Leftrightarrow x=\sqrt[]{\left(1+\dfrac{\sqrt[]{127}}{8}\right)^2-\dfrac{3}{4}}+\dfrac{1}{2}\)

\(tanC=\dfrac{AB}{AC}\Rightarrow AC=\dfrac{AB}{tanC}=\dfrac{8}{tan40^o}=9,52\left(cm\right)\)

\(sinC=\dfrac{AB}{BC}\Rightarrow BC=\dfrac{AB}{sinC}=\dfrac{8}{sin40^o}=12,5\left(cm\right)\)

tra gg thui bn ơi

C= \(\dfrac{√x-√y}{xy√xy}\) : 

\(\dfrac{(1}{x})\) + \(\dfrac{(1}{y)}\) . \(\dfrac{1}{x+y+2√xy}\)

+ \(\dfrac{2}{(√x+√y)³}\) . \(\dfrac{(1}{√x)}\) + \(\dfrac{(1}{√y)}\) 

Tính C với x = 2 - √3 ; y = 2+√3

ĐKXĐ : \(x\ne0;x\ne\pm1\)

a) Bạn ghi lại rõ đề.

b) \(B=\dfrac{x-1}{x+1}+\dfrac{3x-x^2}{x^2-1}=\dfrac{x-1}{x+1}+\dfrac{3x-x^2}{\left(x-1\right).\left(x+1\right)}\)

\(=\dfrac{\left(x-1\right)^2+3x-x^2}{\left(x-1\right).\left(x+1\right)}=\dfrac{x+1}{\left(x-1\right).\left(x+1\right)}=\dfrac{1}{x-1}\)

c) \(P=A.B=\dfrac{x^2+x-2}{x.\left(x-1\right)}=\dfrac{\left(x-1\right).\left(x+2\right)}{x\left(x-1\right)}=\dfrac{x+2}{x}=1+\dfrac{2}{x}\)

Không tồn tại Min P \(\forall x\inℝ\)

Lời giải: 
ĐKXĐ: $x\geq 0; x\neq 1$
a.

\(A=\left[\frac{x+2}{(\sqrt{x}-1)(x+\sqrt{x}+1)}+\frac{\sqrt{x}(\sqrt{x}-1)}{(\sqrt{x}-1)(x+\sqrt{x}+1)}-\frac{x+\sqrt{x}+1}{(\sqrt{x}-1)(x+\sqrt{x}+1)}\right].\frac{2}{\sqrt{x}-1}\)

\(=\frac{x+2+x-\sqrt{x}-(x+\sqrt{x}+1)}{(\sqrt{x}-1)(x+\sqrt{x}+1)}.\frac{2}{\sqrt{x}-1}\)

\(=\frac{2(x-2\sqrt{x}+1)}{(\sqrt{x}-1)^2(x+\sqrt{x}+1)}=\frac{2(\sqrt{x}-1)^2}{(\sqrt{x}-1)^2(x+\sqrt{x}+1)}=\frac{2}{x+\sqrt{x}+1}\)

b.

Ta thấy với $x\geq 0 ; x\neq 1$ thì $x+\sqrt{x}+1\geq 1$

$\Rightarrow A=\frac{2}{x+\sqrt{x}+1}\leq 2$

Vậy $A$ đạt max bằng $2$ khi $x=0$

đkxđ: \(x\ge-\dfrac{1}{3}\)

pt đã cho tương đương với

\(\left(x-1\right)^2=\sqrt{3x+1}-\sqrt{x^2+x+2}\)

\(\Rightarrow\sqrt{3x+1}\ge\sqrt{x^2+x+2}\)

\(\Rightarrow3x+1\ge x^2+x+2\)

\(\Leftrightarrow x^2-2x+1\le0\)

\(\Leftrightarrow\left(x-1\right)^2\le0\)

\(\Leftrightarrow x-1=0\)

\(\Leftrightarrow x=1\) (nhận)

Vậy, pt đã cho có nghiệm duy nhất \(x=1\)

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