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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,5mũ 36=(5mũ3)mũ12=125 mũ12
11^24=(11^2)12=121^12
vì 121<125 nên 5^36>11^24
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
1; 73.52.54.76:(55.78)
= (73.76).(52.54) : (55.78)
= 79.56: (55.78)
= (79:78).(56:55)
= 7.5
= 35
2; 33.a7.3.a2:(34.a6)
= (33.3).(a7.a2): (34.a6)
= 34.a9: (34.a6)
= (34:34).(a9:a6)
= a3
a,\(\frac{7}{10}\cdot\frac{4}{9}+\frac{3}{10}\cdot\frac{4}{9}-1\frac{7}{9}\)
\(=\frac{14}{45}+\frac{2}{15}-\frac{16}{9}\)
\(=\frac{14}{45}+\frac{6}{45}-\frac{80}{45}\)
\(=\frac{-60}{45}=\frac{-4}{3}\)
b,\(\frac{-5}{6}+\frac{4}{9}\cdot\left(\frac{5}{4}-\frac{2}{3}\right)\cdot\left(-3\right)^2+\frac{5}{9}\cdot30\%\)
\(=\frac{-5}{6}+\frac{4}{9}\cdot\left(\frac{7}{12}\right)\cdot9+\frac{5}{9}\cdot\frac{3}{10}\)
\(=\frac{-5}{6}+\frac{7}{3}+\frac{1}{6}\)
\(=\frac{-5}{6}+\frac{14}{6}+\frac{1}{6}\)
=\(=\frac{10}{6}=\frac{5}{3}\)
Câu c:
1/2017.(1/3 - 7/12 + 1/4) - (6 2/3 - 1,5.2^2) :5/6
= 1/2017.(4/12 - 7/12 + 3/12) - (20/3 - 1,5x 4) : 5/6
= 1/2017.0 - (20/3 - 6) x 6/5
= 0 - (20/3 - 18/3) x 6/5
= - 2/3 x 6/5
= - 4/5
k nha
Bài 1.
a) 123.33=(12.3)3=363.123.33=(12.3)3=363.
b) 25.84=25.(23)4=25.212=217.25.84=25.(23)4=25.212=217.
c) 38.90.272=38.1.(33)2=38.36=314.38.90.272=38.1.(33)2=38.36=314.
d) 24.54=(2.5)4=104.24.54=(2.5)4=104.
e)
Trả lời :
56 : 54 + 23 . 22 - 225 : 152
= 56 - 4 + 23 + 2 - 152 : 152
= 52 + 25 - 1
= 25 + 32 - 1
= 56
632
75:72+46:43+225
=73+43+225
=343+64+225
=407+225
=632
7^5:7^2+4^6:4^3+225
=343+64+225
=632
thank you