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\(\sqrt{4x-2\sqrt{4x-1}}+\sqrt{4x+2\sqrt{4x-1}}\)(với \(x\ge\dfrac{1}{4}\))
\(=\sqrt{\left(\sqrt{4x-1}-1\right)^2}+\sqrt{\left(\sqrt{4x-1}+1\right)^2}\)
\(=\left(\sqrt{4x-1}-1\right)+\left(\sqrt{4x-1}+1\right)\)
\(=2\sqrt{4x-1}\) (với \(x\ge\dfrac{1}{4}\))
Làm nốt ::v
\(2.3\sqrt{\left(a-2\right)^2}=3\text{ |}a-2\text{ |}=3\left(a-2\right)\left(a< 2\right)\)
\(3.\sqrt{81a^4}+3a^2=\sqrt{3^4.a^4}+3a^2=9a^2+3a^2=12a^2\)
\(4.\sqrt{64a^2}+2a=\text{ |}8a\text{ |}+2a=8a+2a=10a\left(a>=0\right)\)
\(6.\sqrt{a^2+6a+9}+\sqrt{a^2-6a+9}=\sqrt{\left(a+3\right)^2}+\sqrt{\left(a-3\right)^2}=\text{ |}a+3\text{ |}+\text{ |}a-3\text{ |}\)
\(7.\dfrac{\sqrt{1-2x+x^2}}{x-1}=\dfrac{\sqrt{\left(x-1\right)^2}}{x-1}=\dfrac{\text{ |}x-1\text{ |}}{x-1}\)
\(8.\dfrac{\sqrt{9x^2-6x+1}}{9x^2-1}=\dfrac{\sqrt{\left(3x-1\right)^2}}{\left(3x-1\right)\left(3x+1\right)}=\dfrac{\text{ |}3x-1\text{ |}}{\left(3x-1\right)\left(3x+1\right)}\)
\(9.4-x-\sqrt{4-4x+x^2}=4-x-\sqrt{\left(x-2\right)^2}=4-x-\text{ |}x-2\text{ |}\)
Mình làm ba câu mẫu, bạn theo đó mà làm các câu còn lại.
Giải:
1) \(2\sqrt{a^2}\)
\(=2\left|a\right|\)
\(=2a\left(a\ge0\right)\)
Vậy ...
5) \(3\sqrt{9a^6}-6a^3\)
\(=3\sqrt{\left(3a^3\right)^2}-6a^3\)
\(=3.3a^3-6a^3\)
\(=9a^3-6a^3\)
\(=3a^3\)
Vậy ...
10) \(C=\sqrt{4x^2-4x+1}-\sqrt{4x^2+4x+1}\)
\(\Leftrightarrow C=\sqrt{\left(2x-1\right)^2}-\sqrt{\left(2x+1\right)^2}\)
\(\Leftrightarrow C=2x-1^2-\left(2x+1^2\right)\)
\(\Leftrightarrow C=2x-1-2x-1\)
\(\Leftrightarrow C=-2\)
Vậy ...
Đặt \(D=\sqrt{2x+\sqrt{4x-1}}-\sqrt{2x-\sqrt{4x-1}}\) (D >/ 0 với mọi 1/2 < x)
\(\Rightarrow D^2=2\sqrt{4x-1}-2\sqrt{4x^2-4x+1}=2\sqrt{4x-1}-2\left|2x-1\right|=2\sqrt{4x-1}-2\left(1-2x\right)=4x-2+2\sqrt{4x-1}\)
\(\Rightarrow D=\sqrt{D^2}=\sqrt{4x-2+2\sqrt{4x-1}}=\left|\sqrt{4x-1}+1\right|=\sqrt{4x-1}+1\)
\(A=\frac{\sqrt{\left(x-1\right)^2}}{x-1}-\frac{\sqrt{\left(x-2\right)^2}}{x-2}=\frac{\left|x-1\right|}{x-1}-\frac{\left|x-2\right|}{x-2}\)
+) Nếu x < 1 => A = \(\frac{-\left(x-1\right)}{x-1}-\frac{-\left(x-2\right)}{x-2}=-1-\left(-1\right)=0\)
+) Nếu 1 < x < 2 => A = \(\frac{\left(x-1\right)}{x-1}-\frac{-\left(x-2\right)}{x-2}=1-\left(-1\right)=2\)
+) Nếu x > 2 => A = \(\frac{\left(x-1\right)}{x-1}-\frac{\left(x-2\right)}{x-2}=1-1=0\)
Tớ làm nốt nè :3
\(1b.3\sqrt{2}+4\sqrt{8}-\sqrt{18}=3\sqrt{2}+8\sqrt{2}-3\sqrt{2}=8\sqrt{2}\)
\(c.\dfrac{1}{2+\sqrt{3}}+\dfrac{1}{2-\sqrt{3}}=\dfrac{2-\sqrt{3}+2+\sqrt{3}}{\left(2-\sqrt{3}\right)\left(2+\sqrt{3}\right)}=4\)
\(2a.\sqrt{4x^2-4x+1}=3\)
\(\Leftrightarrow4x^2-4x+1=9\)
\(\Leftrightarrow4x^2+4x-8x-8=0\)
\(\Leftrightarrow4\left(x+1\right)\left(x-2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=2\end{matrix}\right.\)
\(b.\sqrt{4x-4}-\sqrt{9x-9}+5\sqrt{x-1}=7\left(x\ge1\right)\)
\(\Leftrightarrow2\sqrt{x-1}-3\sqrt{x-1}+5\sqrt{x-1}=7\)
\(\Leftrightarrow4\sqrt{x-1}=7\)
\(\Leftrightarrow\sqrt{x-1}=\dfrac{7}{4}\)
\(\Leftrightarrow x=\dfrac{65}{16}\)
c. Sai đề.
\(=\sqrt{4x-1-2\sqrt{4x-1}+1}+\sqrt{4x-1+2\sqrt{4x-1}+1}\)
\(=\sqrt{\left(\sqrt{4x-1}-1\right)^2}+\sqrt{\left(\sqrt{4x-1}+1\right)^2}\)
\(=\left|\sqrt{4x-1}-1\right|+\sqrt{4x-1}+1\)
\(=\left[{}\begin{matrix}2\sqrt{4x-1}\text{ nếu }x\ge\dfrac{1}{2}\\2\text{ nếu }\dfrac{1}{4}\le x< \dfrac{1}{2}\end{matrix}\right.\)