Question

[Ánh Dương]

1.a) Rút gọn: \(\frac{2x+\sqrt{x}-1}{1-x}+\frac{2x\sqrt{x}+x-\sqrt{x}}{1+x\sqrt{x}}\)

b) \(\sqrt[3]{3+\sqrt{17}}+\sqrt[3]{3-\sqrt{17}}\)

2. Giải phương trình:

a) \(\sqrt{x^2-3x+2}+\sqrt{x+3}=\sqrt{x-2}+\sqrt{x^2+2x-3}\)

b) \(\sqrt{2x^2-9x+4}+3\sqrt{2x-1}=\sqrt{2x^2+21x-11}\)

c) \(x^2+2015x-2014=2\sqrt{2017x-2016}\)

d) \(\sqrt{\left(1+x^2\right)^3}-4x^3=1-3x^4\)

Answer 1

[Nguyễn Việt Lâm]

1/

a/ ĐKXĐ: ...

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

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

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

Câu b không rút gọn được, lập phương lên thì biểu thức là nghiệm của pt \(x^3+6x-6=0\) ko có nghiệm đẹp

Bài 2:

a/ ĐKXĐ: \(x\ge2\)

\(\Leftrightarrow\sqrt{\left(x-1\right)\left(x-2\right)}-\sqrt{x-2}-\sqrt{\left(x-1\right)\left(x+3\right)}+\sqrt{x+3}=0\)

\(\Leftrightarrow\sqrt{x-2}\left(\sqrt{x-1}-1\right)-\sqrt{x+3}\left(\sqrt{x-1}-1\right)=0\)

\(\Leftrightarrow\left(\sqrt{x-2}-\sqrt{x+3}\right)\left(\sqrt{x-1}-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x-1}=1\\\sqrt{x-2}=\sqrt{x+3}\left(vn\right)\end{matrix}\right.\) \(\Rightarrow x=2\)

Answer 2

[Nguyễn Việt Lâm]

2/

b/

\(\Leftrightarrow\sqrt{\left(x-4\right)\left(2x-1\right)}+3\sqrt{2x-1}=\sqrt{\left(x+11\right)\left(2x-1\right)}\)

Để phương trình đã cho xác định thì:

\(\left\{{}\begin{matrix}\left(x-4\right)\left(2x-1\right)\ge0\\2x-1\ge0\\\left(x+11\right)\left(2x-1\right)\ge0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}\left[{}\begin{matrix}x\ge4\\x\le\frac{1}{2}\left(1\right)\end{matrix}\right.\\x\ge\frac{1}{2}\left(2\right)\end{matrix}\right.\)

Từ (1) và (2) \(\Rightarrow x=\frac{1}{2}\) thay vào pt thấy thỏa mãn

Vậy \(x=\frac{1}{2}\) là nghiệm duy nhất

c/ ĐKXĐ: ...

\(\Leftrightarrow x^2-2x+1+2017x-2016-2\sqrt{2017x-2016}+1=0\)

\(\Leftrightarrow\left(x-1\right)^2+\left(\sqrt{2017x-2016}-1\right)^2=0\)

\(\Leftrightarrow\left\{{}\begin{matrix}x-1=0\\\sqrt{2017x-2016}-1=0\end{matrix}\right.\) \(\Rightarrow x=1\)

d/ \(\Leftrightarrow\sqrt{\left(1+x^2\right)^3}-1+3x^4-4x^3=0\)

\(\Leftrightarrow\frac{\left(1+x^2\right)^3-1}{\left(1+x^2\right)^3+1}+x^2\left(3x^2-4x\right)=0\)

\(\Leftrightarrow\frac{x^6+3x^4+3x^2}{\left(1+x^2\right)^2+1}+x^2\left(3x^2-4x\right)=0\)

\(\Leftrightarrow x^2\left(\frac{x^4+3x^3+3}{x^4+2x^2+2}+3x^2-4x\right)=0\)

\(\Rightarrow x=0\)