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5 tháng 10 2019

Ta có:A=2+22+23+...+220

=>2A=2(2+22+23+...+220)

2A=4+23+24+...+221

=>2A-A=(4+23+24+...+221)-(2+22+23+...+220)

A=221-2

5 tháng 10 2019

A= 2.( 2+ 2+ 3+ 4+ 5+ 6+ 7+8 +9 + 10= 11+ 12+ 13+ 14+15+ 16+ 17+ 18+ 19+ 20)

A=2.211

A= 422

B= 5.(1+ 5+ 2+ 3+ 4+ 5+ 6+ 7+ 8+ 9+..........+30)

B= 5. 470

B= 2350 

15 tháng 7 2021

\(0,05+5-\dfrac{1}{20}=0,05+5-0,05=5\)

\(\dfrac{6}{15}-\dfrac{7}{8}+3+\dfrac{3}{5}-\dfrac{2}{16}=\dfrac{2}{.5}-\dfrac{7}{8}+3+\dfrac{3}{5}-\dfrac{1}{8}=1-1+3=3\)

 

a) \(0.05+5-\dfrac{1}{20}=\dfrac{1}{20}+5-\dfrac{1}{20}=5\)

b) \(\dfrac{6}{15}-\dfrac{7}{8}+3+\dfrac{3}{5}-\dfrac{2}{16}=1-1+3=3\)

12 tháng 3 2022

undefined

11 tháng 2 2023

`#lv`

`-2/5+(-7/10)-9/6`

`=-2/5-7/10-9/6`

`=-4/10-7/10-9/6`

`=-11/10-3/2`

`=-11/10-15/10`

`=-26/10`

`=-13/5`

__

`1/2+(-2/5)-(-2/3)`

`=1/2-2/5+2/3`

`=5/10-4/10+2/3`

`=1/10+2/3`

`=3/30+20/30`

`=23/30`

__

`5/3-3/4+7/6`

`=20/12-9/12+14/12`

`=11/12+14/12`

`=25/12`

__

`-1/5+5/3-3/2`

`=-3/15+25/15-3/2`

`=22/15-3/2`

`=44/30-45/30`

`=-1/30`

__

`1/4-7/8+(-9/10)`

`=2/8-7/8-9/10`

`=-5/8-9/10`

`=-25/40-36/40`

`=-61/40`

__

`5/4+1/2+(-7/12)`

`=15/12+6/12-7/12`

`=21/12-7/12`

`=14/12`

`=7/6`

__

`-5/8-1/3+(-7/6)`

`=-5/8-1/3-7/6`

`=-15/24-8/24-28/24`

`=-52/24`

`=-13/6`

__

`-3/4-7/10+(-5/6)`

`=-3/4-7/10-5/6`

`=-45/60-42/60-50/60`

`=-137/60`

11 tháng 2 2023

Bài làm

a, (-2/5) + (-7/10) - 9/6 =(-12/30) + (-21/30) - 45/30=(-33/30) - 45/30 = (-78/30)

b,1/2 + (-2/5) - (-2/3) = 15/30 + (-12/30) - (-20/30) = 3/30 - (-20/30) = 23/30

c,5/3 - 3/4 + 7/6 = 40/24 - 18/24 + 28/24 = 22/24 + 28/24 = 50/24 = 25/12

d, (-1/5) + 5/3 - 3/2 = (-6/30) + 50/30 - 45/30 = 44/30 - 45/30 = (-1/30)

e, 1/4 - 7/8 + (-9/10) = 10/40 - 35/40 - 36/40 = (-25/40) - 36/40 = (-61/40)

f, 5/4 +1/2 + (-7/12) = 15/12 + 6/12 - 7/12 = 21/12 - 7/12 = 14/127/6

g,(-5/8) -1/3 + (-7/6) = (-15/24) - 8/24 - 28/24 = (-23/24) - 28/24 = (-51/24) 

k,(-3/4) - 7/10 + (-5/6) = (-45/60) - 42/60 - 50/60 = (-87/60) - 50/60 = (-137/60)

chúc bn học tốt nha

sai thì mn góp ý giúp mk

 

10 tháng 8 2023

a) \(4\times\dfrac{1}{4^2}+25\times\left[\dfrac{3^3}{4^3}:\dfrac{5^3}{4^3}\right]:\dfrac{3^3}{2^3}\)

\(=\dfrac{1}{4}+5^2\times\dfrac{3^3}{4^3}\times\dfrac{4^3}{5^3}\times\dfrac{2^3}{3^3}\)

\(=\dfrac{1}{4}+\dfrac{2^3}{5}=\dfrac{1}{4}+\dfrac{8}{5}=\dfrac{37}{20}\)

b) \(2^3+3\times\left(\dfrac{1}{2}\right)^{0-1}+\left[\left(-2\right)^2:\dfrac{1}{2}\right]-8\)

\(=8+3\times\left(2^{-1}\right)^{-1}+2^2\times2-8\)

\(=3\times2+2^3=14\)

Muộn rùi ngủ thôi không mai lớn có một khúc à :v 

AH
Akai Haruma
Giáo viên
10 tháng 8 2023

Bạn nên viết đề bằng công thức toán (biểu tượng $\sum$ góc trái khung soạn thảo) để được hỗ trợ tốt hơn nhé. Viết thế này người đọc đề sẽ rất mệt.

6 tháng 8 2017

A = \(\dfrac{2}{5}:\dfrac{3}{4}+\dfrac{2}{5}.\dfrac{3}{6}+\dfrac{2}{5}\)

A=\(\dfrac{2}{5}.\dfrac{4}{3}+\dfrac{2}{5}.\dfrac{3}{6}+\dfrac{2}{5}\)

A=\(\dfrac{2}{5}.\left(\dfrac{4}{3}+\dfrac{3}{6}+1\right)\) =\(\dfrac{2}{5}.\dfrac{17}{6}\)= \(\dfrac{17}{5}\)

B = \(\dfrac{5}{21}.\dfrac{4}{11}+\dfrac{7}{11}.\dfrac{5}{21}-\dfrac{2}{3}\)

B =\(\dfrac{5}{21}\left(\dfrac{4}{11}+\dfrac{7}{11}\right)-\dfrac{2}{3}\)

B= \(\dfrac{5}{21}.1-\dfrac{2}{3}\) = \(\dfrac{5}{21}-\dfrac{2}{3}=\dfrac{-3}{7}\)

20 tháng 6 2018

Ta có :

a, \(\frac{31}{12}-(\frac{2}{5}+x)=\frac{2}{3}\)

\(\Rightarrow\frac{2}{5}+x=\frac{31}{12}-\frac{2}{3}=\frac{23}{12}\)

\(\Rightarrow\frac{23}{12}-\frac{31}{12}=\frac{-8}{12}=\frac{-2}{3}\)

Câu b để mk làm sau

20 tháng 6 2018

ờ bn , giup mk đik r mk kick cho

11 tháng 2 2023

\(a,\dfrac{1}{2}-\dfrac{1}{3}-\left(-\dfrac{5}{4}\right)=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{5}{4}=\dfrac{1\times6-1\times4+5\times3}{12}=\dfrac{6-4+15}{12}=\dfrac{17}{12}\\ b,\dfrac{5}{4}-\dfrac{1}{2}-\dfrac{7}{8}=\dfrac{5\times2-1\times4-7}{8}=\dfrac{10-4-7}{8}=-\dfrac{1}{8}\\ c,\dfrac{1}{5}-\dfrac{1}{2}+\dfrac{9}{10}=\dfrac{1\times2-1\times5+9}{10}=\dfrac{2-5+9}{10}=\dfrac{6}{10}=\dfrac{3}{5}\\ d,\dfrac{5}{4}-\dfrac{1}{3}+\dfrac{7}{6}=\dfrac{5\times3-1\times4+7\times2}{12}=\dfrac{15-4+14}{12}=\dfrac{25}{12}\)

11 tháng 2 2023

`1/2+(-1/3)-(-5/4)`

`=1/2-1/3+5/4`

`=3/6-2/6+5/4`

`=1/6+5/4`

`=2/12+15/12`

`=17/12`

__

`5/4-1/2+(-7/8)`

`=5/4-1/2-7/8`

`=10/8-4/8-7/8`

`=6/8-7/8`

`=-1/8`

__

`1/5-1/2+9/10`

`=2/10-5/10+9/10`

`=-3/10+9/10`

`=6/10`

`=3/5`

__

`5/4-1/3+7/6`

`=15/12-4/12+14/12`

`=11/12+14/12`

`=25/12`

`#lv`

6 tháng 3 2020

Tính:

\(\frac{2}{3}+\frac{3}{4}=\frac{8}{12}+\frac{9}{12}=\frac{17}{12}\)

\(\frac{1}{5}+\frac{3}{2}=\frac{2}{10}+\frac{15}{10}=\frac{17}{10}\)

\(\frac{6}{5}-\frac{2}{3}=\frac{18}{15}-\frac{10}{15}=\frac{8}{15}\)

\(\frac{7}{2}-\frac{3}{4}=\frac{14}{4}-\frac{3}{4}=\frac{11}{4}\)

\(1\frac{2}{5}+\frac{7}{2}=\frac{7}{5}+\frac{7}{2}=\frac{14}{10}+\frac{35}{10}=\frac{49}{10}\)

\(2\frac{1}{8}-\frac{5}{6}=\frac{17}{8}-\frac{5}{6}=\frac{51}{24}-\frac{20}{24}=\frac{31}{24}\)

\(0,75+2\frac{1}{3}=\frac{3}{4}+\frac{7}{3}=\frac{9}{12}+\frac{28}{12}=\frac{37}{12}\)

\(1-\frac{1}{4}-0,25=1-\frac{1}{4}-\frac{1}{4}=\frac{4}{4}-\frac{1}{4}-\frac{1}{4}=\frac{2}{4}=\frac{1}{2}\)

\(\frac{11}{2}-\frac{5}{3}+\frac{7}{4}=\frac{66}{12}-\frac{20}{12}+\frac{21}{12}=\frac{67}{12}\)

\(\frac{5}{6}+1\frac{2}{3}-\frac{1}{4}=\frac{5}{6}+\frac{5}{3}-\frac{1}{4}=\frac{10}{12}+\frac{20}{12}-\frac{3}{12}=\frac{27}{12}=\frac{9}{4}\)

\(0,5+2\frac{3}{5}-\frac{5}{4}=\frac{1}{2}+\frac{13}{5}-\frac{5}{4}=\frac{10}{20}+\frac{52}{20}-\frac{25}{20}=\frac{37}{20}\)

\(3\frac{1}{2}-\frac{5}{6}+1,2=\frac{7}{2}-\frac{5}{6}+\frac{6}{5}=\frac{105}{30}-\frac{25}{30}+\frac{36}{30}=\frac{116}{30}=\frac{58}{15}\)

\(\frac{1}{3}+2\frac{1}{4}=\frac{1}{3}+\frac{9}{4}=\frac{4}{12}+\frac{27}{12}=\frac{31}{12}\)

\(\frac{7}{2}+\frac{3}{4}+\frac{7}{12}=\frac{42}{12}+\frac{9}{12}+\frac{7}{12}=\frac{58}{12}=\frac{29}{6}\)

\(2-\frac{4}{9}-\frac{1}{6}=\frac{36}{18}-\frac{8}{18}-\frac{3}{18}=\frac{25}{18}\)

Chúc bạn hok tốt !!! ღℓїŋɦ✿şʉŋღ