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#)Giải :
\(\left(\frac{1}{2}\right)^{15}\div\left(\frac{1}{4}\right)^{20}=\left(\frac{1}{2}\right)^{15}\div\left(\frac{1}{2}\right)^{40}=\left(\frac{1}{2}\right)^{-25}\)
Bài 2:
Ta thấy: 52 > 4.5
62 > 5.6
72 > 6.7
....
20172 > 2016.2017
\(\Rightarrow\)\(\frac{1}{5^2}< \frac{1}{4.5}\)
\(\frac{1}{6^2}< \frac{1}{5.6}\)
\(\frac{1}{7^2}< \frac{1}{6.7}\)
....
\(\frac{1}{2017^2}< \frac{1}{2016.2017}\)
Cộng vế với nhau, ta có:
\(\frac{1}{5^2}+\frac{1}{6^2}+\frac{1}{7^2}+...+\frac{1}{2017^2}\) < \(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{2016.2017}\)
\(\Rightarrow\)A < \(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{2016}-\frac{1}{2017}\)
\(\Rightarrow\)A < \(\frac{1}{4}-\frac{1}{2017}\)
\(\Rightarrow\)A < \(\frac{1}{4}\)( vì \(\frac{1}{2017}>0\))
k giúp mik ✅
Bài 1:
- 2 2/15 .3/8 - (7/20 - 75%) : 8/5
= -32/15.3/8 - (7/20 - 3/4) x 5/8
= - 4/5 - (7/20 - 15/20) x 5/8
= - 4/5 + 8/20 x 5/8
= - 4/5 + 1/4
= - 16/20 + 5/20
= - 11/20
a. \(\frac{1}{5}+\frac{3}{4}+\frac{1}{10}\)
= \(\frac{4}{20}+\frac{15}{20}+\frac{2}{20}\)
= \(\frac{21}{20}\)
b. \(\frac{5}{6}-\frac{1}{3}+\frac{1}{6}\)
= \(\frac{5}{6}-\frac{2}{6}+\frac{1}{6}\)
= \(\frac{4}{6}=\frac{2}{3}\)
c. \(\frac{3}{8}-\frac{10}{2}:\frac{4}{5}\)
= \(\frac{3}{8}-\frac{50}{8}\)
= \(\frac{-47}{8}\)
a) \(\frac{1}{5}+\frac{3}{4}+\frac{1}{10}\)
= \(\frac{4+15+2}{20}\)
= \(\frac{21}{20}\)
b) \(\frac{5}{6}-\frac{1}{3}+\frac{1}{6}\)
= \(\frac{5-2+1}{6}\)
= \(\frac{4}{6}\)
c) \(\frac{3}{8}-\frac{10}{2}:\frac{4}{5}\)
= \(\frac{3}{8}-\frac{25}{4}\)
= \(-\frac{47}{8}\)
a) \(176+483+24+117=\left(176+24\right)+\left(483+117\right)=200+600=800\)
b) \(5^6:5^4-2^3-3^0=5^2-8-1=17-1=16\)
c) \(27.62+27.39-27=27.\left(62+39-1\right)=27.100=2700\)
Câu a:
7/10.4/9 + 3/10.4/9 - 1 7/9
= 4/9.(7/10 + 3/10) - 16/9
= 4/9 - 16/9
= - 12/9
= - 4/3
Câu b:
- 5/6 + 4/9.(5/4 - 2/3).(-3)^2 + 5/9.30%
= - 5/6 + [5/9 - 8/27].9 + 5/9.3/10
= - 5/6 + 5 - 8/3 + 1/6
= (-5/6 + 1/6) - 8/3 + 5
= - 4/6 - 8/3 + 15/3
= - 2/3 - 8/3 + 15/3
= - 10/3 + 15/3
= 5/3
Câu a:
A = 7 2/13 - (5 2/13 + 2 1/2)
A = 7 2/13 - 5 2/13 - 2 1/2
A = 2 - 2 1/2
A = 2 - 2 - 1/2
A = 0 - 1/2
A = -1/2
Câu b:
B = - 3/4 + 25% : (10 3/10 - 9 4/5) - (-1/2)^2
B = - 3/4 + 1/4 : (103/10 - 49/5) - 1/4
B = - 3/4 + 1/4 : (103/10 - 98/5) - 1/4
B = (-3/4 - 1/4) + 1/4 : (1/2)
B = -1 + 1/4 x 2/1
B = -1 + 1/2
B = - 1/2
Câu a:
A = 7 2/13 - (5 2/13 + 2 1/2)
A = 7 2/13 - 5 2/13 - 2 1/2
A = 2 - 2 1/2
A = 2 - 2 - 1/2
A = 0 - 1/2
A = -1/2
Câu b:
B = - 3/4 + 25% : (10 3/10 - 9 4/5) - (-1/2)^2
B = - 3/4 + 1/4 : (103/10 - 49/5) - 1/4
B = - 3/4 + 1/4 : (103/10 - 98/5) - 1/4
B = (-3/4 - 1/4) + 1/4 : (1/2)
B = -1 + 1/4 x 2/1
B = -1 + 1/2
B = - 1/2
\(\frac{-1}{3}:\frac{-5}{6}=\frac{-1}{3}\times\frac{-6}{5}=\frac{2}{5}\)
@muối
(-1/3) : (-5/6) = 2/5
\(\frac{-1}{3}:\frac{-5}{6}\)
\(=\frac{-1}{3}.\frac{6}{-5}\)
\(=\frac{-6}{-15}\)
\(=\frac{-2}{-5}\)
\(=\frac{2}{5}\)