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a)
= \(\sqrt{18-6\sqrt{6}+3}\)
= \(\sqrt{\left(3\sqrt{2}\right)^2-2\cdot3\sqrt{2}\cdot\sqrt{3}+\left(\sqrt{3}\right)^2}\)
= \(\sqrt{\left(3\sqrt{2}-\sqrt{3}\right)^2}\)
= \(|3\sqrt{2}-\sqrt{3}|\)
= \(3\sqrt{2}-\sqrt{3}\)
b)
= \(\sqrt{\frac{7}{2}-\sqrt{7}+\frac{1}{2}}\)
= \(\sqrt{\left(\sqrt{\frac{7}{2}}\right)^2+2\cdot\sqrt{\frac{7}{2}}\cdot\sqrt{\frac{1}{2}}+\left(\sqrt{\frac{1}{2}}\right)^2}\)
= \(\sqrt{\left(\sqrt{\frac{7}{2}}+\sqrt{\frac{1}{2}}\right)^2}\)
= \(|\sqrt{\frac{7}{2}}+\sqrt{\frac{1}{2}}|\)
= \(\sqrt{\frac{7}{2}}+\sqrt{\frac{1}{2}}\)
c)
= \(\sqrt{3+2\sqrt{3}+1}\)
= \(\sqrt{\left(\sqrt{3}\right)^2+2\cdot\sqrt{3}\cdot1+1^2}\)
= \(\sqrt{\left(\sqrt{3}+1\right)^2}=\sqrt{3}+1\)
d)
Đặt t = \(\sqrt{x-1}\left(ĐK:t\ge0\right)\)
= \(\sqrt{t^2+1-2t}\)
= \(\sqrt{\left(t+1\right)^2}\)
\(=t+1\)
= \(\sqrt{x-1}+1\)
\(\sqrt{21-6\sqrt{6}}=\sqrt{18-2\sqrt{9}\sqrt{6}+3}=\sqrt{\left(\sqrt{18}\right)^2-2\sqrt{18}\sqrt{3}+\left(\sqrt{3}\right)^2}\)
\(=\sqrt{\left(\sqrt{18}+\sqrt{3}\right)^2}=\sqrt{18}+\sqrt{3}=\sqrt{3}+3\sqrt{2}\)
\(\sqrt{4-\sqrt{7}}=\frac{\sqrt{2}\sqrt{4-\sqrt{7}}}{\sqrt{2}}=\frac{\sqrt{8-2\sqrt{7}}}{\sqrt{2}}=\frac{\sqrt{7-2\sqrt{7}+1}}{\sqrt{2}}\)
\(=\frac{\sqrt{\left(\sqrt{7}-1\right)^2}}{\sqrt{2}}=\frac{\sqrt{7}-1}{\sqrt{2}}=\frac{\sqrt{14}-\sqrt{2}}{2}\)
\(\sqrt{4+2\sqrt{3}}=\sqrt{3+2\sqrt{3}+1}=\sqrt{\left(\sqrt{3}+1\right)^2}=\sqrt{3}+1\)
Với \(x\ge1\)thì \(\sqrt{x-2\sqrt{x-1}}=\sqrt{\left(x-1\right)-2\sqrt{x-1}+1}\)
\(=\sqrt{\left(\sqrt{x-1}\right)^2-2\sqrt{x-1}\sqrt{1}+\left(\sqrt{1}\right)^2}\)
\(=\sqrt{\left(\sqrt{x-1}-1\right)^2}=\sqrt{x-1}-1\)
T đã tốn mấy phút cuộc đời viết lời giải cho bạn r, tiếc j mấy giây mà bấm k cho t ik =))
a/A\(=\frac{x+2}{x-\sqrt{x}-2}-\frac{2\sqrt{x}}{\sqrt{x}+1}-\frac{1-\sqrt{x}}{\sqrt{x}-2}\)
\(=\frac{x+2-2\sqrt{x}\left(\sqrt{x}-2\right)-\left(1-\sqrt{x}\right)\left(\sqrt{x}+1\right)}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-2\right)}\)
\(=\frac{x+2-2x+4\sqrt{x}-1+x}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-2\right)}\)
\(=\frac{4\sqrt{x}-1}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-2\right)}\)
Thay x=16 vào A ta có: A\(=\frac{3}{2}\)
b/ B= \(1-\frac{\sqrt{x}-3}{\sqrt{x}-2}\)
\(\frac{\sqrt{x}-2-\sqrt{x}+3}{\sqrt{x}-2}=\frac{1}{\sqrt{x}-2}\)
=>C=\(\frac{4\sqrt{x}-1}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-2\right)}:\frac{1}{\sqrt{x}-2}\)=\(\frac{4\sqrt{x}-1}{\sqrt{x}+1}\)
c/Để C thuộc Z thì \(\frac{4\sqrt{x}-1}{\sqrt{x}+1}\) thuộc Z
C\(=\text{}\frac{4\sqrt{x}-1}{\sqrt{x}+1}=\frac{4\sqrt{x}+4}{\sqrt{x}+1}-\frac{5}{\sqrt{x}+1}=4-\frac{5}{\sqrt{x}+1}\)
=> \(5⋮\left(\sqrt{x}+1\right)
\Leftrightarrow\sqrt{x}+1\in\left\{-5;-1;1;5\right\}\)
Nhận xét: \(\sqrt{x}+1\ge1\)
\(\Rightarrow\sqrt{x}+1\in\left\{1;5\right\}\)
\(\Leftrightarrow\sqrt{x}\in\left\{0;4\right\}
\Leftrightarrow x\in\left\{0;16\right\}\)
Vậy \(x\in\left\{0;16\right\}\) thì C thuộc Z
Chúc bạn học tốt!
Em thử nha,sai thì thôi ạ.
2/ ĐK: \(-2\le x\le2\)
PT \(\Leftrightarrow\sqrt{2x+4}-\sqrt{8-4x}=\frac{6x-4}{\sqrt{x^2+4}}\)
Nhân liên hợp zô: với chú ý rằng \(\sqrt{2x+4}+\sqrt{8-4x}>0\) với mọi x thỏa mãn đk
PT \(\Leftrightarrow\frac{6x-4}{\sqrt{2x+4}+\sqrt{8-4x}}-\frac{6x-4}{\sqrt{x^2+4}}=0\)
\(\Leftrightarrow\left(6x-4\right)\left(\frac{1}{\sqrt{2x+4}+\sqrt{8-4x}}-\frac{1}{\sqrt{x^2+4}}\right)=0\)
Tới đây thì em chịu chỗ xử lí cái ngoặc to rồi..
1.\(\left(\sqrt{x+3}-\sqrt{x+1}\right)\left(x^2+\sqrt{x^2+4x+3}\right)=2x\)
ĐK \(x\ge-1\)
Nhân liên hợp ta có
\(\left(x+3-x-1\right)\left(x^2+\sqrt{x^2+4x+3}\right)=2x\left(\sqrt{x+3}+\sqrt{x+1}\right)\)
<=>\(x^2+\sqrt{\left(x+1\right)\left(x+3\right)}=x\left(\sqrt{x+3}+\sqrt{x+1}\right)\)
<=> \(\left(x^2-x\sqrt{x+3}\right)+\left(\sqrt{\left(x+1\right)\left(x+3\right)}-x\sqrt{x+1}\right)=0\)
<=> \(\left(x-\sqrt{x+3}\right)\left(x-\sqrt{x+1}\right)=0\)
<=> \(\orbr{\begin{cases}x=\sqrt{x+3}\\x=\sqrt{x+1}\end{cases}}\)
=> \(x\in\left\{\frac{1+\sqrt{13}}{2};\frac{1+\sqrt{5}}{2}\right\}\)
Vậy \(x\in\left\{\frac{1+\sqrt{13}}{2};\frac{1+\sqrt{5}}{2}\right\}\)
#)Giải :
a) \(A=\left(\frac{\sqrt{x}}{2}-\frac{1}{2\sqrt{x}}\right)\left(\frac{x\sqrt{x}}{\sqrt{x}-1}-\frac{x+\sqrt{x}}{\sqrt{x}-1}\right)\)
\(=\frac{x-1}{2\sqrt{x}}\left(\frac{\sqrt{x}\left(\sqrt{x}-1\right)^2-\sqrt{x}\left(\sqrt{x}+1\right)^2}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}\right)\)
\(=\frac{x-1}{2\sqrt{x}}.\frac{x\sqrt{x}-2x+\sqrt{x}-x\sqrt{x}-2x-\sqrt{x}}{x-1}\)
\(=\frac{-4}{2\sqrt{x}}=-2\sqrt{x}\)
A = \(\frac{8\sqrt{41}}{2\sqrt{2^2+2.2.\sqrt{41}+\sqrt{41}^2}}\)
A = \(\frac{8\sqrt{41}}{2\sqrt{\left(2+\sqrt{41}\right)^2}}\)
A = \(\frac{8\sqrt{41}}{2\left|2+\sqrt{41}\right|}\)
A = \(\frac{8\sqrt{41}}{4+2\sqrt{41}}\)
B = \(\left(\frac{2x+1}{\sqrt{x}^3+1^3}-\frac{1}{\sqrt{x}-1}\right):\frac{x+\sqrt{x}+1+x+4}{x+\sqrt{x}+1}\)
B = \(\left(\frac{2x+1}{\left(\sqrt{x}+1\right)\left(x-\sqrt{x}+1\right)}-\frac{1}{\sqrt{x}-1}\right).\frac{x+\sqrt{x}+1}{2x+\sqrt{x}+5}\)
Bạn tự làm tiếp nhé, mỏi tay quá!!
\(A=\frac{8\sqrt{41}}{2\sqrt{45+4\sqrt{41}}}=\frac{8\sqrt{41}}{2\sqrt{41+4\sqrt{41}+4}}=\frac{8\sqrt{41}}{2\sqrt{\left(\sqrt{41}\right)^2+2\cdot\sqrt{41}\cdot2+2^2}}\)
\(=\frac{8\sqrt{41}}{2\sqrt{\left(\sqrt{41}+2\right)^2}}=\frac{8\sqrt{41}}{2\left(\sqrt{41}+2\right)}=\frac{8\sqrt{41}\left(\sqrt{41}-2\right)}{2\left(41-4\right)}=\frac{328-16\sqrt{41}}{74}=\frac{164-8\sqrt{41}}{37}\)
\(B=\left(\frac{2x+1}{x\sqrt{x}+1}-\frac{1}{\sqrt{x}-1}\right):\left(1-\frac{x+4}{x+\sqrt{x}+1}\right)\)
\(=\left(\frac{2x+1}{\sqrt{x}^3+1^3}-\frac{x+\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\right):\left(\frac{x+\sqrt{x}+1-x-4}{x+\sqrt{x}+1}\right)\)
\(=\left(\frac{2x+1-x-\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\right):\left(\frac{\sqrt{x}-3}{x+\sqrt{x}+1}\right)\)
\(=\frac{x-\sqrt{x}}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\cdot\frac{x+\sqrt{x}+1}{\sqrt{x}-3}\)
\(=\frac{x-\sqrt{x}}{\left(\sqrt{x}-1\right)\left(\sqrt{x}-3\right)}\)
\(=\frac{\sqrt{x}\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(\sqrt{x}-3\right)}=\frac{\sqrt{x}}{\sqrt{x}-3}=\frac{\sqrt{x}\left(\sqrt{x}+3\right)}{x-9}=\frac{x+3\sqrt{x}}{x-9}\)
b, bạn kiểm tra lại đề nhé
c, \(\frac{x\sqrt{x}-8+2x-4\sqrt{x}}{x-4}=\frac{\sqrt{x}\left(x-4\right)+2\left(x-4\right)}{x-4}\)
\(=\frac{\left(\sqrt{x}+2\right)\left(x-4\right)}{x-4}=\sqrt{x}+2\)