Cảm ơn bạn nha # Cấn Thu Ngân nhưng mình biết làm rồi.Cảm ơn bạn nhé!

tính: T= (1-1/2)+(1-1/4)+(1-1/8)+.....+(1-1/512)+(1-1/1024)

Trần Thị Kim Dung, câu của bạn mình biết làm.

Trình bày hết ra thì dài lắm. Mình nói cái chính rồi bạn làm nốt.

Cách 1 ở tất cả các câu: Tính bình thường như đề cho

 a)   Cách 2: \(\frac{5}{7}\times\frac{3}{4}+\frac{5}{7}\times\frac{1}{2}\)

 b) Cách 2: \(\frac{13}{21}\times\left(\frac{5}{7}+\frac{2}{7}\right)\)

c) Cách 2: \(\frac{2}{5}\times\frac{1}{2}+\frac{2}{5}\times\frac{1}{3}\)

d) Cách 2: \(\frac{17}{21}\times\left(5+\frac{2}{5}\right)\)

1) 42/35 - [ 33/14 . 21/22 - ( 54/25 : 27/25 - 7/10 )]

= 42/35 - ( 9/4-13/10)

=42/35-19/20

=1/4

2) a) 5/21 . x/34 = 35/102     

x/34=35/102 : 5/21

x/34=49/34

=> x=34

Vậy x=34

b) 15/x . 21/13 = 45/91

15/x=45/91 : 21/13

15/x=15/49

=> x=49

Vậy x=49

lớp 4

a) \(\frac{3}{5}:\left(-\frac{1}{15}-\frac{1}{6}\right)+\frac{3}{5}:\left(-\frac{1}{3}-1\frac{1}{15}\right)\)

\(=\frac{3}{5}:\left(-\frac{1}{15}-\frac{1}{6}-\frac{2}{6}-1+\frac{1}{15}\right)\)

\(=\frac{3}{5}:\left(-\frac{1}{2}-1\right)\)

\(=\frac{3}{5}:\left(-\frac{3}{2}\right)\)

\(=-\frac{2}{5}\)

b) \(\left(-\frac{3}{4}+\frac{5}{13}\right):\frac{2}{7}-\left(2\frac{1}{4}+\frac{8}{13}\right):\frac{2}{7}\)

\(=\left(-\frac{3}{4}+\frac{5}{13}-2+\frac{1}{4}+\frac{8}{13}\right):\frac{2}{7}\)

\(=\left(-\frac{1}{2}+1-2\right):\frac{2}{7}\)

\(=\left(-\frac{1}{2}-1\right):\frac{2}{7}\)

\(=-\frac{3}{2}:\frac{2}{7}\)

\(=-\frac{21}{4}\)

c) \(\left(\frac{1}{2}-\frac{13}{14}\right):\frac{5}{7}-\left(-\frac{2}{21}+\frac{1}{7}\right):\frac{5}{7}\)

\(=\left(\frac{7}{14}-\frac{13}{14}+\frac{2}{21}-\frac{3}{21}\right):\frac{5}{7}\)

\(=\left(-\frac{3}{7}-\frac{1}{21}\right):\frac{5}{7}\)

\(=\left(-\frac{9}{21}-\frac{1}{21}\right):\frac{5}{7}\)

\(=-\frac{10}{21}:\frac{5}{7}\)

\(=-\frac{2}{3}\)

= -103/273

= 0

= -5/7

5.\(-\dfrac{3}{7}+\dfrac{5}{13}+\dfrac{-4}{12}=-\dfrac{103}{273}\)

b.\(-\dfrac{5}{21}+\dfrac{-2}{21}+\dfrac{8}{24}=\dfrac{-5-2}{21}+\dfrac{8}{24}=-\dfrac{7}{21}+\dfrac{8}{24}=-\dfrac{1}{3}+\dfrac{8}{24}=0\)

c.\(\dfrac{5}{13}+\dfrac{-5}{7}+\dfrac{-20}{41}+\dfrac{8}{13}+\dfrac{-21}{41}=\left(\dfrac{5}{13}+\dfrac{8}{13}\right)+\left(\dfrac{-20}{41}+\dfrac{-21}{41}\right)+-\dfrac{5}{7}=1-1-\dfrac{5}{7}=-\dfrac{5}{7}\)

a) \(\dfrac{7}{5}x\div\left(9-6\dfrac{13}{21}\right)=2\dfrac{13}{25}\)

\(\dfrac{7}{5}x\div\left(9-\dfrac{139}{21}\right)=\dfrac{63}{25}\)

\(\dfrac{7}{5}x\div\dfrac{50}{21}=\dfrac{63}{25}\)

\(\dfrac{7}{5}x=6\)

\(x=\dfrac{30}{7}\)

b) \(\left(1,16-x\right)\times5,25\div\left(10\dfrac{5}{9}-7\dfrac{1}{4}\right)\times2\dfrac{2}{17}=75\%\)

\(\left(1,16-x\right)\times5,25\div\left(\dfrac{95}{9}-\dfrac{29}{4}\right)\times\dfrac{36}{17}=\dfrac{75}{100}\)

\(\left(1,16-x\right)\times5,25\div\dfrac{119}{36}=\dfrac{17}{48}\)

\(\left(1,16-x\right)\times5,25=\dfrac{2023}{1728}\)

\(1,16-x=\dfrac{289}{1296}\)

\(x=0,9370061728\)

52 ×.(y : 78) = 3380

         y : 78   = 3380 : 52

         y : 78   = 65

         y           = 65 ×. 78

         y           = 5070

Đề thiếu vế phải rồi bạn

c \(\dfrac{2}{3}\times\dfrac{13}{4}\times\dfrac{3}{2}\times\dfrac{7}{3}\times\dfrac{4}{7}\)

= \(\dfrac{2\times13\times3\times7\times4}{3\times4\times2\times3\times7}\)

= \(\dfrac{13}{3}\)

\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}\)

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

=\(\dfrac{1}{1}-\dfrac{1}{5}\)

=\(\dfrac{4}{5}\)

a, (\(\dfrac{41}{25}\) + \(\dfrac{17}{100}\)) + \(\dfrac{39}{25}\)

= (\(\dfrac{41}{25}\) + \(\dfrac{39}{25}\)) + \(\dfrac{17}{100}\) 

= \(\dfrac{80}{25}\) + \(\dfrac{17}{100}\)

= \(\dfrac{320}{100}\) + \(\dfrac{17}{100}\)

= \(\dfrac{337}{100}\)

g, \(\dfrac{1}{12}\) + \(\dfrac{1}{20}\) + \(\dfrac{1}{30}\) + \(\dfrac{1}{42}\)

= \(\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+\dfrac{1}{6\times7}\)

= \(\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}\)

= \(\dfrac{1}{3}-\dfrac{1}{7}\)

= \(\dfrac{7}{21}-\dfrac{3}{21}\)

= \(\dfrac{4}{21}\)

3+5/21=3/1+5/21=68/21

5-13/7=22/7

5/7×4=20/7

4:1/5=?20

k mk nhé

# chikute #

3+\(\frac{5}{21}\)=\(\frac{68}{21}\)

5-\(\frac{13}{7}\)=\(\frac{22}{7}\)

\(\frac{5}{7}\)*4=\(\frac{20}{7}\)

4:\(\frac{1}{5}\)=20

Í lộn

5-13/17