minh ghi nhầm, dấu căn dưới mẫu là bao trùm luôn -7x+3 nhen

\(x=1+\sqrt[3]{2}+\sqrt[3]{4}=\frac{1}{\sqrt[3]{2}-1}.\)

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

\(\Rightarrow x^3-3x^2-3x-1=0\)

\(\Rightarrow\hept{\begin{cases}x^3+x^2+5x+3=4\left(x+1\right)^2\\x^3-2x^2-7x+3=\left(x-2\right)^2\end{cases}}\)

Khi đó:

\(P=\frac{2\left(x+1\right)-6}{x-2}=2\)(do x>0)

cái cuối là do x>2 nhá mình nhầm

mình ghi nhầm, dấu căn dưới mẫu là bao trùm luôn -7x+3 nhen

Bấm máy

Thí dụ ra 2, chứng minh tử=2.mẫu là xong

Đây là phương pháp tối ưu nhất để "ăn gian" khi làm dạng bài kiểu này

chỉ được một thôi mà

^.^

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

\(x^3-3x^2+3x-1=6+6x-6\)

\(x^3-3x^2-3x-1=0\)

\(x^3+x^2+5x+3-4x^2-8x-4=0\)

\(x^3+x^2+5x+3=4\left(x+2\right)^2\)

\(\sqrt{x^3+x^2+5x+3}=2|x+2|\)

Còn lại tương tự nha bạn

\(x-1=\sqrt[3]{4}+\sqrt[3]{2}\)

\(\Rightarrow x^3-3x^2+3x-1=6+3\sqrt[3]{8}\left(\sqrt[3]{2}+\sqrt[3]{4}\right)\)

\(\Rightarrow x^3-3x^2+3x-1=6+6\left(x-1\right)\)

\(\Rightarrow x^3-3x^2-3x-1=0\)

\(\Rightarrow x^3=3x^2+3x+1\)

\(P=\frac{\sqrt{3x^2+3x+1+x^2+5x+3}-6}{\sqrt{3x^2+3x+1-2x^2-7x+3}}=\frac{\sqrt{4\left(x+1\right)^2}-6}{\sqrt{\left(x-2\right)^2}}\)

\(=\frac{2x-4}{x-2}=2\)

@Vũ Minh Tuấn @Nguyễn Việt Lâm @Lê Thị Thục Hiền

ĐK: \(x-9\ne0\Rightarrow x\ne9\)

\(\sqrt{x}\ge0\Rightarrow x\ge0\)

\(x+\sqrt{x}-6\ne0\Rightarrow x+3\sqrt{x}-2\sqrt{x}-6\ne0\Rightarrow\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)\ne0\)

\(\Rightarrow\sqrt{x}-2\ne0\Rightarrow\sqrt{x}\ne2\Rightarrow x\ne4\)

ĐKXĐ: \(x\ge0;x\ne4;x\ne9\)

\(A=\left(\frac{x-3\sqrt{x}}{x-9}\right):\left(\frac{1}{x+\sqrt{x}-6}+\frac{\sqrt{x}-3}{\sqrt{x}-2}-\frac{\sqrt{x}-2}{\sqrt{x}+3}\right)\)

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

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

\(=\frac{\sqrt{x}}{\sqrt{x}+3}:\frac{1+x-9-x+4\sqrt{x}-4}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}\)

\(=\frac{\sqrt{x}}{\sqrt{x}+3}.\frac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+3\right)}{4\sqrt{x}-12}\)

\(=\frac{\sqrt{x}\left(\sqrt{x}-2\right)}{4\left(\sqrt{x}-3\right)}\)

2, Với \(x=\frac{25}{16}\)\(\Rightarrow\sqrt{x}=\sqrt{\frac{25}{16}}=\frac{5}{4}\)

\(A=\frac{\frac{5}{4}\left(\frac{5}{4}-2\right)}{4\left(\frac{5}{4}-3\right)}=\frac{5}{4}.\left(-\frac{3}{4}\right):4\left(-\frac{7}{4}\right)=-\frac{15}{16}:-7=\frac{15}{112}\)

\(\orbr{\begin{cases}\orbr{\begin{cases}\\\end{cases}}\\\end{cases}}\)\(\orbr{\begin{cases}\orbr{\begin{cases}\sqrt{x}-2< 0\\\sqrt{x}-3>0\end{cases}\Rightarrow\orbr{\begin{cases}\sqrt{x}< 2\\\sqrt{x}>3\end{cases}}\Rightarrow\orbr{\begin{cases}x< 4\\x>9\end{cases}}}\\\orbr{\begin{cases}\sqrt{x}-2>0\\\sqrt{x}-3< 0\end{cases}\Rightarrow\orbr{\begin{cases}\sqrt{x}>2\\\sqrt{x}< 3\end{cases}\Rightarrow\orbr{\begin{cases}x>4\\x< 9\end{cases}}}}\end{cases}}\)

\(R=\left[\frac{2\sqrt{x}}{\sqrt{x}+3}+\frac{\sqrt{x}}{\sqrt{x}-3}-\frac{3\left(\sqrt{x}+3\right)}{x-9}\right]:\left(\frac{2\sqrt{x}-2}{\sqrt{x}-3}-1\right)\)

a/ \(R=\left[\frac{2\sqrt{x}}{\sqrt{x}+3}+\frac{\sqrt{x}}{\sqrt{x}-3}-\frac{3\left(\sqrt{x}+3\right)}{\left(\sqrt{x}+3\right)\left(\sqrt[]{x-3}\right)}\right]:\left(\frac{2\sqrt{x}-2-\sqrt{x}+3}{\sqrt{x}-3}\right)\)

=> \(R=\left[\frac{2\sqrt{x}}{\sqrt{x}+3}+\frac{\sqrt{x}}{\sqrt{x}-3}-\frac{3}{\sqrt[]{x-3}}\right]:\frac{\sqrt{x}+1}{\sqrt{x}-3}\)

=> \(R=\left[\frac{2\sqrt{x}}{\sqrt{x}-3}+1\right]:\frac{\sqrt{x}+1}{\sqrt{x}-3}\)

=> \(R=\left[\frac{2\sqrt{x}+\sqrt{x}-3}{\sqrt{x}-3}\right].\frac{\sqrt{x}-3}{\sqrt{x}+1}\)

=> \(R=\frac{3\sqrt{x}-3}{\sqrt{x}-3}.\frac{\sqrt{x}-3}{\sqrt{x}+1}=\frac{3\left(\sqrt{x}-1\right)}{\sqrt{x}+1}\)

b/ Để R<-1   => \(\frac{3\left(\sqrt{x}-1\right)}{\sqrt{x}+1}< -1\)

<=> \(3\sqrt{x}-3< -\sqrt{x}-1\)

<=> \(4\sqrt{x}< 2\)=> \(\sqrt{x}< \frac{1}{2}\) => \(-\frac{1}{4}< x< \frac{1}{4}\)

Chỗ => R = \(\left(\frac{2\sqrt{x}}{\sqrt{x}-3}+1\right):\frac{\sqrt{x}+1}{\sqrt{x}-3}\)   là sao vậy ạ?

Thì \(\frac{\sqrt{x}}{\sqrt{x}-3}-\frac{3}{\sqrt{x}-3}=\frac{\sqrt{x}-3}{\sqrt{x}-3}=1\)