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10 tháng 3 2018

\(B=\dfrac{5}{10.11}+\dfrac{5}{11.12}+\dfrac{5}{12.13}+...+\dfrac{5}{19.20}\)

\(\Rightarrow\dfrac{B}{5}=\dfrac{1}{10.11}+\dfrac{1}{11.12}+\dfrac{1}{12.13}+...+\dfrac{1}{19.20}\)

\(=\dfrac{1}{10}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{13}+...+\dfrac{1}{19}-\dfrac{1}{20}\)

\(=\dfrac{1}{10}-\dfrac{1}{20}=\dfrac{2}{20}-\dfrac{1}{20}=\dfrac{1}{20}\)

\(\Rightarrow B=\dfrac{1}{20}.5=\dfrac{5}{20}=\dfrac{1}{4}\)

a) Ta có: \(-19-\left|+13\right|+\left|-10\right|-\left(-5\right)-11\)

\(=-19-13+10+5-11\)

\(=-28\)

b) Ta có: \(\left(-10\right)-\left(11\right)+\left|-5\right|-\left|-7\right|-8\)

\(=-10-11+5-7-8\)

\(=-31\)

c) Ta có: \(-\left(-8\right)-\left(+7\right)-\left|-11\right|+\left|+12\right|\)

\(=8-7-11+12\)

\(=2\)

d) Ta có: \(-14-\left|-18\right|-\left(-20\right)-\left|-25\right|\)

\(=-14-18+20-25\)

\(=-37\)

đ) Ta có: \(23-\left|-15\right|-\left(-17\right)+\left|-13\right|\)

\(=23-15+17+13\)

\(=38\)

19 tháng 2

a; A = -1 + 3 - 5 + 7 - 9 + 11 - 13 + 15 - 17

   A = (-1 + 11) + ( 3 - 13) + (-5 + 15) + (7 - 17) - 9

   A = 10 - 10 + 10 - 10 - 9

 A = (10 - 10) + (10 - 10) - 9

 A = 0 + 0 - 9

A = -9 

19 tháng 2

b; B = 1+2-3-4+5+6-7-8+9+10-11-12+13+14-15-16+17+18-19-20

B = (1+2-3-4) + (5+6-7-8)+(9+10-11-12)+(13+14-15-16)+(17+18-19-20)

B= -4+(-4)+(-4)+(-4)+(-4) 

B= -4 . 5

B= -20

1: =72/90+65/90=137/90

2: =24/56-77/56=-53/56

3: =-7/10+4/5=1/10

4: =15/100-4/100=11/100

5: =4/6-5/6=-1/6

6: =10/40-15/40-76/40=-81/40

7: =-9/10+7/18

=-81/90+35/90=-46/90=-23/45

8: =27/90-55/90=-28/90=-14/45

9: =36/60-50/60-35/60=-49/60

10: =-4/9+5/6-3/8

=-32/72+60/72-27/72

=1/72

25 tháng 1 2022

a, \(=\dfrac{2}{9}-\dfrac{10}{10}=\dfrac{2}{9}-1=-\dfrac{7}{9}\)

b, \(=-\dfrac{12}{6}+\dfrac{2}{5}=-2+\dfrac{2}{5}=-\dfrac{8}{5}\)

c, \(=\dfrac{27}{13}-1=\dfrac{14}{13}\)

d, \(=\dfrac{12}{11}+\dfrac{7}{19}+\dfrac{12}{19}=\dfrac{12}{11}+1=\dfrac{23}{11}\)

25 tháng 1 2022

a) \(\dfrac{2}{9}+\dfrac{-3}{10}+\dfrac{-7}{10}\)

\(=\dfrac{2}{9}+\dfrac{-10}{10}=\dfrac{2}{9}-1=-\dfrac{7}{9}\)

b) \(\dfrac{-11}{6}+\dfrac{2}{5}+\dfrac{-1}{6}\)

\(=-2+\dfrac{2}{5}=-\dfrac{8}{5}\)

BÀI 1

a,  \(5\times\frac{-7}{10}=\frac{-35}{10}=\frac{-7}{2}\)

b,  \(\frac{4}{5}\times\frac{-7}{10}=\frac{-28}{50}=\frac{-14}{25}\)

c,  \(\frac{4}{9}+\frac{4}{3}\times\frac{16}{4}=\frac{4}{9}+\frac{16}{3}=\frac{52}{9}\)

d,  \(\frac{11}{22}-\frac{3}{9}\times\frac{14}{21}=\frac{11}{22}-\frac{2}{9}=\frac{55}{198}=\frac{5}{18}\)  

BÀI 2

\(A=\frac{6}{13}\times\frac{5}{7}+\frac{6}{13}\times\frac{2}{7}+\frac{17}{13}\)

\(A=\frac{30}{91}+\frac{12}{91}+\frac{17}{13}\)

\(A=\frac{30}{91}+\frac{12}{91}+\frac{119}{91}\)

\(A=\frac{161}{91}=\frac{23}{13}\)

\(B=\frac{11}{15}\times\frac{4}{11}+\frac{11}{15}\times\frac{5}{11}+\frac{11}{15}\times\frac{2}{11}\)

\(B=\frac{4}{15}+\frac{1}{3}+\frac{2}{15}\)

\(B=\frac{11}{15}\)

\(C=\left(\frac{19}{64}-\frac{33}{22}+\frac{24}{51}\right)\times\left(\frac{1}{5}-\frac{1}{15}-\frac{2}{15}\right)\)

\(C=\frac{-797}{1088}\times0\)

\(C=0\)

\(D=\frac{8}{13}\times\frac{7}{12}+\frac{8}{13}\times\frac{5}{12}-\frac{1}{12}\)

\(D=\frac{14}{39}+\frac{10}{39}-\frac{1}{12}\)

\(D=\frac{83}{156}\)

3 tháng 10 2021

bạn biết câu náy không (24 + 11) . {546 - [14 . (64 - 2^{3}3) : 2]} =

6 tháng 3 2020

a)\(\frac{3^{10}.\left(-5\right)^{21}}{\left(-5\right)^{20}.3^{12}}=\frac{-5}{9}\)

b)\(\frac{\left(-11\right)^5.13^7}{11^5.13^8}=-\frac{1}{13}\)

c)\(\frac{2^{10}.3^{10}-2^{10}.3^9}{2^9.3^{10}}=\frac{2^{10}.3^9\left(3-1\right)}{2^9.3^{10}}=2\)

d(\(\frac{5^{11}.7^{12}+5^{11}.7^{11}}{5^{12}.7^{12}+9.5^{11}.7^{11}}=\frac{5^{11}.7^{11}\left(7+1\right)}{5^{11}.7^{11}\left(35+9\right)}=\frac{1}{6}\)

7 tháng 3 2020

giúp mk vs nha

a. ( 23 - 21) + ( 19 - 17) + ( 15 - 13) + ( 11 - 9) + ( 7 - 5) + ( 3 - 1) 

= 2 + 2 + 2 + 2 + 2 + 2 

= 2 x 6

= 12

b. ( 24 - 22 ) + ( 20 - 18 ) + ( 16 - 14 ) + ( 12 - 10) + ( 8 - 6 ) + ( 4 - 2) 

= 2 + 2 + 2 + 2 + 2 + 2 

= 2 x 6 

= 12

19 tháng 2

A = - 1 + 3 - 5 + 7 - 9 + 11 - 13 + 15 - 17

A = (-1 + 11) + (3 -  13) + (7- 17) + (-5 + 15) - 9

= - 10 + 10 - 10 + 10 - 9

= (-10 + 10) + (-10 + 10) - 9

= 0 + 0 - 9

= - 9

19 tháng 2

B = 1+2-3-4+5+6-7-8+9+10-11-12+13+14-15-16+17+18-19-20

B =(1+2-3-4)+(5+6-7-8)+(9+10-11-12)+(13+14-15-16)+(17+18-19-20)

B = -4+ (-4) + (-4) + (-4) + (-4) 

B = -4 x 5

B = -20