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2²⁰ = (2⁵)⁴ = 32⁴
3¹² = (3³)⁴ = 27⁴
Do 32 > 27 nên 32⁴ > 27⁴
Vậy 2²⁰ > 3¹²
220 = (25)4 = 324
312 = (33)4 = 274
Vì 32 > 27 ⇒ 324 > 274 ⇒ 220 > 312
227 = (23)9 = 89
318 = ( 32)9 = 99
Vì 9 > 8 nên : 99 > 89
Vậy suy ra: 318 > 227
Ta có :
- 9999=101.99\(\Rightarrow\)999910=(101.99)10=10110.9910
- 9920=9910+10=9910.9910
Vì 10110>9910\(\Leftrightarrow\)10110.9910>9910.9910\(\Leftrightarrow\)999910>9920
Vậy 999910>9920
\(A=\left(\dfrac{1}{4}-1\right).\left(\dfrac{1}{9}-1\right)....\left(\dfrac{1}{100}-1\right).\)
\(\Rightarrow A=\left(-\dfrac{3}{4}\right).\left(-\dfrac{8}{9}\right)....\left(-\dfrac{99}{100}\right)\)
mà A có 9 dấu - \(\left(4;9;16;25;36;49;64;81;100\right)\)
\(\Rightarrow0>A=\left(-\dfrac{3}{4}\right).\left(-\dfrac{8}{9}\right)....\left(-\dfrac{99}{100}\right)=-\dfrac{1}{2}\)
Ta lại có \(\left\{{}\begin{matrix}\dfrac{1}{2}=\dfrac{21}{42}\\\dfrac{11}{21}=\dfrac{22}{42}\end{matrix}\right.\) \(\Rightarrow\dfrac{1}{2}< \dfrac{11}{21}\Rightarrow-\dfrac{1}{2}>-\dfrac{11}{21}\)
\(\Rightarrow A>-\dfrac{11}{21}\)
\(A=\left(\dfrac{1}{4}-1\right)\left(\dfrac{1}{9}-1\right)...\left(\dfrac{1}{100}-1\right)\)
\(A=\left(-\dfrac{2^2-1}{2^2}\right)\left(-\dfrac{3^2-1}{3^2}\right)...\left(-\dfrac{10^2-1}{10^2}\right)\)
\(A=\left[-\dfrac{1\cdot3}{2\cdot2}\right]\left[-\dfrac{2\cdot4}{3\cdot3}\right]...\left[-\dfrac{9\cdot11}{10\cdot10}\right]\)
Dễ thấy A có 9 thừa số, suy ra
\(A=-\dfrac{1\cdot3\cdot2\cdot4\cdot...\cdot9\cdot11}{2\cdot2\cdot3\cdot3\cdot...\cdot10.10}=-\dfrac{1\cdot11}{2\cdot10}=\dfrac{-11}{20}\)
Vì 20 < 21 nên \(\dfrac{11}{20}>\dfrac{11}{21}\), suy ra \(\dfrac{-11}{20}< \dfrac{-11}{21}\)
Vậy \(A< \dfrac{-11}{21}\)
b, ( \(\dfrac{1}{6}\))2.62 + \(\dfrac{\left(0,6\right)^5}{\left(0,2\right)^6}\)
= (\(\dfrac{6}{6}\))2 + ( \(\dfrac{0,6}{0,2}\))5. \(\dfrac{1}{0,2}\)
= 1 + 35. \(\dfrac{1}{0,2}\)
= 1 + 1215
= 1216
\(8^{15}=\left(2^3\right)^{15}=2^{3.15}=2^{45}\\ 16^4=\left(2^4\right)^4=2^{4.4}=2^{16}\\ 2^{45}>2^{16}\Rightarrow8^{15}>16^4\)
Cảm ơn bạn nhiều.