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18 tháng 12 2016

a.ta có: \(3^{2009}\)

\(9^{1005}\)= \(\left(3^2\right)^{1005}\) =\(3^{2010}\)

*Vì 2010> 2009 =>\(3^{2009}\) < \(3^{2010}\)

Vậy \(3^{2009}\) < \(9^{1005}\).

6 tháng 11 2019

\(\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{100^2}< \frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}=\)

\(=\frac{2-1}{1.2}+\frac{3-2}{2.3}+\frac{4-3}{3.4}+...+\frac{100-99}{99.100}=\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{99}-\frac{1}{100}=1-\frac{1}{100}< 1\)

22 tháng 10 2020

A) \(\left(\frac{1}{3}\right)^{^2}.\frac{1}{3}.9^2=3=3^1\)(viết dưới dạng lũy thừa)

B)\(8< 2^n< 2.16\)

\(2^3< 2^n< 2.2^4\)

\(2^3< 2^n< 2^5\)

\(\Rightarrow3< n< 5\)

mà n là số tự nhiên => n = 4

C) |-x| = 1 => |x| = 1 => x = -1 hoặc x = 1.

|2x| = 6.7 + (-3,3) - 0.4 = 42 - 3,3 - 0 = 42 - 3,3 = 38,7

=> 2x = 38,7 hoặc 2x = -38,7

=> x = 19,35 hoặc x = -19,35

28 tháng 12 2020

Lớp 6 nha!

9 tháng 9 2017

a, (-1/5)n=-1/125

=> (-1/5)n=(-1/5)3

=> n=3

b, (-2/11)m=4/121

=> (-2/11)m=(2/11)2

=> m=2

9 tháng 9 2017

\(\left(\frac{-1}{5}\right)^n=\frac{-1}{125}\)

\(\Rightarrow\frac{-1}{5^n}=\frac{1}{125}\)

=> 125 = 5n = 53 <=> n = 3

\(\left(\frac{-2}{11}\right)^m=\frac{4}{121}\)

\(\Rightarrow\frac{-2}{11^m}=\frac{4}{121}\)

=> 11m = 121 = 112 <=> m = 2

16 tháng 7 2015

\(\text{a)}A=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{n^2}

6 tháng 8 2018

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