3 căn x =15
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1 tháng 8 2018
1/
Ta có: \(\left(1+\sqrt{15}\right)^2\)= 1 + 15 + \(2\sqrt{15}\)= 16 + \(2\sqrt{15}\)
\(\sqrt{24}^2\)= 24 = 16 + 8
Vì: \(\sqrt{15}^2\)= 15 < 16 =\(4^2\)
Nên: \(\sqrt{15}< 4\)
=> \(2\sqrt{15}< 8\)
=> \(16+2\sqrt{15}< 24\)
=> \(\left(1+\sqrt{15}\right)^2< \sqrt{24}^2\)
Vậy \(1+\sqrt{15}< \sqrt{24}\)
2/
b/ \(3x-7\sqrt{x}=20\)\(\left(x\ge0\right)\)
<=> \(3x-7\sqrt{x}-20=0\)
<=> \(3x-12\sqrt{x}+5\sqrt{x}-20=0\)
<=> \(3\sqrt{x}\left(\sqrt{x}-4\right)+5\left(\sqrt{x}-4\right)=0\)
<=> \(\left(\sqrt{x}-4\right)\left(3\sqrt{x}+5\right)=0\)
<=> \(\sqrt{x}-4=0\)hoặc \(3\sqrt{x}+5=0\)
<=> \(\sqrt{x}=4\)hoặc \(3\sqrt{x}=-5\)(vô nghiệm)
<=> \(x=16\)
Vậy S=\(\left\{16\right\}\)
c/ \(1+\sqrt{3x}>3\)
<=> \(\sqrt{3x}>2\)
<=> \(3x>4\)
<=> \(x>\frac{4}{3}\)
d/ \(x^2-x\sqrt{x}-5x-\sqrt{x}-6=0\)(\(x\ge0\))
<=> \(\left(x^2-5x-6\right)-\left(x\sqrt{x}+\sqrt{x}\right)=0\)
<=> \(\left(x^2-6x+x-6\right)-\left(x\sqrt{x}+\sqrt{x}\right)=0\)
<=> \([x\left(x-6\right)+\left(x-6\right)]-\sqrt{x}\left(x+1\right)=0\)
<=> \(\left(x-6\right)\left(x+1\right)-\sqrt{x}\left(x+1\right)=0\)
<=> \(\left(x+1\right)\left(x-6-\sqrt{x}\right)=0\)
<=> \(\left(x+1\right)\left(x-3\sqrt{x}+2\sqrt{x}-6\right)=0\)
<=> \(\left(x+1\right)[\sqrt{x}\left(\sqrt{x}-3\right)+2\left(\sqrt{x}-3\right)]=0\)
<=> \(\left(x+1\right)\left(\sqrt{x}-3\right)\left(\sqrt{x}+2\right)=0\)
<=> \(x+1=0\) hoặc \(\sqrt{x}-3=0\)hoặc \(\sqrt{x}+2=0\)
<=> \(x=-1\)(loại) hoặc \(x=9\)hoặc \(\sqrt{x}=-2\)(vô nghiệm)
Vậy S={ 9 }
22 tháng 7 2020
1) Ta có: \(\frac{x+6\sqrt{x}+9}{x-9}=\frac{\left(\sqrt{x}+3\right)^2}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}=\frac{\sqrt{x}+3}{\sqrt{x}-3}\)
H9
HT.Phong (9A5)
CTVHS
23 tháng 8 2023
a) \(15\sqrt{\dfrac{4}{3}}-5\sqrt{48}+2\sqrt{12}-6\sqrt{\dfrac{1}{3}}\)
\(=\sqrt{15^2\cdot\dfrac{4}{3}}-5\cdot4\sqrt{3}+2\cdot2\sqrt{3}-\sqrt{6^2\cdot\dfrac{1}{3}}\)
\(=\sqrt{\dfrac{225\cdot4}{3}}-20\sqrt{3}+4\sqrt{3}-\sqrt{\dfrac{36}{3}}\)
\(=\sqrt{75\cdot4}-16\sqrt{3}-\sqrt{12}\)
\(=10\sqrt{3}-16\sqrt{3}-2\sqrt{3}\)
\(=-8\sqrt{3}\)
b) \(\dfrac{15}{\sqrt{6}+1}-\dfrac{3}{\sqrt{7}-\sqrt{2}}-15\sqrt{6}+3\sqrt{7}\)
\(=\dfrac{15\left(\sqrt{6}-1\right)}{\left(\sqrt{6}+1\right)\left(\sqrt{6}-1\right)}-\dfrac{3\left(\sqrt{7}+\sqrt{2}\right)}{\left(\sqrt{7}-\sqrt{2}\right)\left(\sqrt{7}+\sqrt{2}\right)}-15\sqrt{6}+3\sqrt{7}\)
\(=\dfrac{15\left(\sqrt{6}-1\right)}{6-1}-\dfrac{3\sqrt{7}+3\sqrt{2}}{7-2}-15\sqrt{6}+3\sqrt{7}\)
\(=3\left(\sqrt{6}-1\right)-\dfrac{3\sqrt{7}+3\sqrt{2}}{5}-15\sqrt{6}+3\sqrt{7}\)
\(=3\sqrt{6}-3-\dfrac{3\sqrt{7}+3\sqrt{2}}{5}-15\sqrt{6}+3\sqrt{7}\)
\(=-12\sqrt{6}-3+3\sqrt{7}-\dfrac{3\sqrt{7}+3\sqrt{2}}{5}\)
\(=\dfrac{-60\sqrt{6}-15+15\sqrt{7}-3\sqrt{7}-3\sqrt{2}}{5}\)
\(=\dfrac{-60\sqrt{6}-15+12\sqrt{7}-3\sqrt{2}}{5}\)
\(3\sqrt{x}=15\)
\(\Leftrightarrow\sqrt{x}=5\)
\(\Leftrightarrow x=5^2\)
\(\Leftrightarrow x=25\)
Vậy x = 25
\(3\sqrt{x}=15\)
\(\Leftrightarrow\sqrt{x}=5\)
\(\Leftrightarrow x=5^2\)
\(\Leftrightarrow x=25\)
\(k\)\(nha\)