So sánh 4 và 1+2√3
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1) \(5^{199}< 5^{200}=25^{100}\)
\(3^{300}=27^{100}>25^{100}\)
\(\Rightarrow3^{300}>5^{199}\)
\(\Rightarrow\dfrac{1}{3^{300}}< \dfrac{1}{5^{199}}\)
2) a) \(107^{50}=\left(107^2\right)^{25}=11449^{25}\)
\(73^{75}=\left(73^3\right)^{25}=389017^{25}>11449^{25}\)
\(\Rightarrow107^{50}< 73^{75}\)
b) \(54^4< 5^{12}< 21^{12}\Rightarrow54^4< 21^{12}\)
a) \(\dfrac{3}{4}=0.75\)
b) \(-2\dfrac{1}{2}=\dfrac{-5}{2}< \dfrac{-5}{3}\)
\(1+\dfrac{1}{3}+1\dfrac{3}{4}\div2\dfrac{1}{2}+\dfrac{2}{3}\)
\(=1+\dfrac{1}{3}+\dfrac{7}{4}\div\dfrac{5}{2}+\dfrac{2}{3}\)
\(=1+\dfrac{1}{3}+\dfrac{7}{10}+\dfrac{2}{3}\)
\(=\left(1+\dfrac{7}{10}\right)+\left(\dfrac{1}{3}+\dfrac{2}{3}\right)\)
\(=\dfrac{17}{10}+1\)
\(=\dfrac{27}{10}\)
Bài 1:
a) \(\dfrac{-17}{36}\) và \(\dfrac{23}{-48}\)
\(\dfrac{-17}{36}=\dfrac{-17.4}{36.4}=\dfrac{-68}{144}\)
\(\dfrac{23}{-48}=\dfrac{-23}{48}=\dfrac{-23.3}{144.3}=\dfrac{-69}{144}\)
Vì \(\dfrac{-68}{144}>\dfrac{-69}{144}\) nên \(\dfrac{-17}{36}>\dfrac{23}{-48}\)
b) \(\dfrac{-1}{3}\) và \(\dfrac{2}{5}\)
Vì \(\dfrac{-1}{3}\) là số âm mà \(\dfrac{2}{5}\) là số dương nên \(\dfrac{-1}{3}< \dfrac{2}{5}\)
c) \(\dfrac{2}{7}\) và \(\dfrac{5}{4}\)
Vì \(\dfrac{2}{7}< 1\) mà \(\dfrac{5}{4}>1\) nên \(\dfrac{2}{7}< \dfrac{5}{4}\)
d) \(\dfrac{267}{-268}\) và \(\dfrac{-1347}{1343}\)
\(\dfrac{267}{-268}=\dfrac{-267}{268}=\dfrac{-267.449}{268.449}=\dfrac{-119883}{120332}\)
\(\dfrac{-1347}{1343}=\dfrac{-1347.89}{1343.89}=\dfrac{-119883}{119527}\)
Vì \(\dfrac{-119883}{120332}>\dfrac{-119883}{119527}\) nên \(\dfrac{267}{-268}>\dfrac{-1347}{1343}\)
Bài 2:
\(\dfrac{5}{2}-\left(1\dfrac{3}{7}-0,4\right)=\dfrac{5}{2}-\dfrac{10}{7}-\dfrac{2}{5}=\dfrac{47}{70}\)
\(\left(1+2+3+4\right)^2=\left(1+2+3+4\right)\left(1+2+3+4\right)=1^2+1\cdot2+1\cdot3+1\cdot4+2\cdot1+2^2+2\cdot3+2\cdot4+3\cdot1+3\cdot2+3^2+3\cdot4+4\cdot1+4\cdot2+4\cdot3+4^2=1^2+2^2+3^2+4^2+1\cdot2+1\cdot3+1\cdot4+2\cdot1+2\cdot3+2\cdot4+3\cdot1+3\cdot2+3\cdot4+4\cdot1+4\cdot2+4\cdot3>1^2+2^2+3^2+4^2\)
a: \(\left(1+2+3+4\right)^2=10^2=100\)
\(1^3+2^3+3^3+4^3=1+8+27+64=100\)
Do đó: \(\left(1+2+3+4\right)^2=1^3+2^3+3^3+4^3\)
b: \(19^4=130321\)
\(16\cdot18\cdot20\cdot22=126720\)
mà 130321>126720
nên \(19^4>16\cdot18\cdot20\cdot22\)
ta có:
\(1+2\sqrt{3}=1+2+\sqrt{3}=1+2+1,73..=4,73...\)
\(\Rightarrow1+2\sqrt{3}>4\)
Ta có: \(2\sqrt{3}=3,464...\)\(>3\)
\(\Rightarrow1+2\sqrt{3}>1+3=4\)
\(Vậy\)\(1+2\sqrt{3}>4\)