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a.
\(A=\frac{1}{2\sqrt{3}-2}-\frac{1}{2\sqrt{3}+2}\\ =\frac{2\sqrt{3}+2-2\sqrt{3}+2}{\left(2\sqrt{3}+2\right)\left(2\sqrt{3}-2\right)}\\ =\frac{4}{\left(2\sqrt{3}\right)^2-2^2}=\frac{4}{8}=\frac{1}{2}\)
\(B=\frac{\sqrt{x}}{\sqrt{x}-1}-\frac{2\sqrt{x}-1}{x-\sqrt{x}}\left(ĐK:x>0;x\ne1\right)\\ =\frac{\left(\sqrt{x}\right)^2}{\sqrt{x}\left(\sqrt{x}-1\right)}-\frac{2\sqrt{x}-1}{\sqrt{x}\left(\sqrt{x}-1\right)}\\ =\frac{x-2\sqrt{x}+1}{\sqrt{x}\left(\sqrt{x}-1\right)}\\ =\frac{\left(\sqrt{x}-1\right)^2}{\sqrt{x}\left(\sqrt{x}-1\right)}=\frac{\sqrt{x}-1}{\sqrt{x}}\)
b.
\(B=\frac{2}{5}A\Leftrightarrow\frac{\sqrt{x}-1}{\sqrt{x}}=\frac{2}{5}\cdot\frac{1}{2}=\frac{1}{5}\\ \Leftrightarrow\frac{\sqrt{x}-1}{\sqrt{x}}-\frac{1}{5}=0\\ \Leftrightarrow\frac{5\left(\sqrt{x}-1\right)-\sqrt{x}}{5\sqrt{x}}=0\\ \Leftrightarrow\frac{4\sqrt{x}-5}{5\sqrt{x}}=0\\ \Rightarrow4\sqrt{x}-5=0\\ \Leftrightarrow\sqrt{x}=\frac{5}{4}\Rightarrow x=\frac{25}{16}\)
(Bạn kiểm tra xem kết quả số có đúng ko nha)
a) Khi \(x=4+2\sqrt{3}\)
\(A=\frac{2\sqrt{\left(\sqrt{3}+1\right)^2}+1}{3\sqrt{\left(\sqrt{3}+1\right)^2}+1}=\frac{2\sqrt{3}+3}{3\sqrt{3}+4}\)
b) \(B=\left(\frac{1}{\sqrt{x}-1}+\frac{\sqrt{x}}{x-1}\right):\left(\frac{\sqrt{x}}{\sqrt{x}-1}-1\right)=\frac{\sqrt{x}+1+\sqrt{x}}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}:\frac{\sqrt{x}-\sqrt{x}+1}{\sqrt{x}-1}=\frac{2\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}.\left(\sqrt{x}-1\right)=\frac{2\sqrt{x}+1}{\sqrt{x}+1}\)
c) Nhác quá tự làm nhé
a) ĐKXĐ: \(\left\{{}\begin{matrix}x\ge0\\x\ne9\end{matrix}\right.\)
\(B=\frac{\sqrt{x}-1}{\sqrt{x}-3}-\frac{7\sqrt{x}-9}{x-9}\\ =\frac{\left(\sqrt{x}-1\right)\left(\sqrt{x}+3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}-\frac{7\sqrt{x}-9}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\\ =\frac{x+3\sqrt{x}-\sqrt{x}-3-7\sqrt{x}+9}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\\ =\frac{x-5\sqrt{x}+6}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\\ =\frac{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}=\frac{\sqrt{x}-2}{\sqrt{x}+3}\)
b) ĐKXĐ: x>0
\(x=\frac{1}{\sqrt{2}-1}-\frac{1}{\sqrt{2}+1}=\frac{\sqrt{2}+1-\sqrt{2}+1}{\left(\sqrt{2}-1\right)\left(\sqrt{2}+1\right)}=\frac{2}{\left(\sqrt{2}\right)^2-1}=\frac{2}{2-1}=2\)
\(\Rightarrow A=\frac{\sqrt{x}-2}{\sqrt{x}}=\frac{\sqrt{2}-2}{\sqrt{2}}=\frac{\sqrt{2}\left(1-\sqrt{2}\right)}{\sqrt{2}}=1-\sqrt{2}\)
c)
\(P=\frac{A}{B}=\frac{\frac{\sqrt{x}-2}{\sqrt{x}+3}}{\frac{\sqrt{x}-2}{\sqrt{x}}}=\frac{\sqrt{x}-2}{\sqrt{x}+3}\cdot\frac{\sqrt{x}}{\sqrt{x}-2}=\frac{\sqrt{x}}{\sqrt{x}+3}\)
Còn khúc sau ko hiểu cho lắm ._.