a) 1-5+7-8+4-1+5-7+8

=(1-1) - (-5+5) -(7-7) -(-8+8) +4

=0

b)=-39+9

=-30

c)=(20-20)-(-4+4)-(8-8)-17+15

=-2

d)= (13-13)-(-98+98)-(91-91)-75

=-75

    \(\frac{1}{2}+\frac{1}{2}.\frac{1}{3}+\frac{1}{3}.\frac{1}{4}+\frac{1}{4}.\frac{1}{5}+...+\frac{1}{9}.\frac{1}{10}\)

\(=\frac{1}{2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\)

\(=\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{10}\)

\(=\frac{1}{2}+\frac{1}{2}-\frac{1}{10}\)

\(=\frac{9}{10}\)

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) \(\frac{3}{8}-\frac{10}{2}:\frac{4}{5}\)

 = \(\frac{3}{8}-\frac{25}{4}\)

 = \(-\frac{47}{8}\)

b,1/5+3/4+1/10

=4/20+15/20+2/20

=21/20

a,5/6-1/3+5/6

5/6-2/6+5/6

=8/6

=4/3

c,3/8-10/2:4/5

=3/8-25/3

-191/24

nhớ k nha

\(\frac{1.3.5+2.6.10+4.12.20+7.21.35}{1.5.7+2.10.14+4.20.28+7.35.49}\)

\(=\frac{1.3.5\left(1+2+4+7\right)}{1.5.7\left(1+2+7+7\right)}=\frac{1.3.5}{1.5.7}=\frac{15}{35}=\frac{3}{7}\)

\(\frac{1\cdot3\cdot5+2\cdot6\cdot10+4\cdot12\cdot20+7\cdot21\cdot35}{1\cdot5\cdot7+2\cdot10\cdot14+4\cdot20\cdot28+7\cdot35\cdot49}\)

\(=\)\(\frac{1\cdot3\cdot5\cdot\left(1+2+4+7\right)}{1\cdot5\cdot7\cdot\left(1+2+7+7\right)}\)

\(=\frac{1\cdot3\cdot5}{1\cdot5\cdot7}\)\(=\frac{15}{35}=\frac{3}{7}\)

bn vội quá viết nhầm lun kìa 

hj hj chúc bn làm bài tốt nha

a) 13 . 58 . 4 + 32 . 26 . 2 + 52 . 10                  b) 53 . 51 + 4 + 53 . 49 + 91 + 53

= 52 . 58 + 32 . 52 + 52 . 10                              = 53 . 55 + 53 . 145 + 53 . 1

= 52. ( 58 + 32 + 10 )                                        = 53 . ( 55 + 145 + 1 )

= 52 . 100                                                          = 53 . 201

= 52000                                                             =  10653

 ~ Chúc bn hok tốt ~

câu b có đúng ko vậyNguyễn Thanh Vân

= (1+99) + (3 + 97) + ( 5 + 95 ) + ....... + ( 49 + 51 )

có tất cả 25 cặp

= 100 x 25 = 2500

Nhớ k mình nhé! Thanks bạn

(1+99)+(3+97)+....+(49+51)=100+100+...+100=5000

Luu y:co 50 so 100

mk thieu la:5000:2=2500 vi co 25 cap

có cần cóp nguyên bài thế k

=1 nha ban

Ta có : 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 + 10 - 11 - 12+......+ 2006 - 2007 - 2008 + 2009 

= (1 + 2 - 3 - 4) + (5 + 6 - 7 - 8) + (9 + 10 - 11 - 12)+...... + (2005 + 2006 - 2007 - 2008) + 2009 

= -4 + -4 + ...... + (-4) + 2009

= (-4) x 502 + 2009

= (-2008) + 2009

= 1

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

`=1/5 . 4/7 + 3/7 . 1/5 -1/5 . 1`

`=1/5 . ( 4/7+3/7-1)`

`=1/5 . ( 7/7-1)`

`= 1/5 . 0`

`=0`

\(\dfrac{1}{5}\times\dfrac{4}{7}+\dfrac{3}{7}\times\dfrac{1}{5}-\dfrac{1}{5}=\dfrac{1}{5}\times\left(\dfrac{4}{7}+\dfrac{3}{7}-1\right)=\dfrac{1}{5}\times0=0\)

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

= \(\dfrac{1}{5}\)+ 0

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

1, Ta có :

     \(x+\frac{3}{5}=\frac{4}{7}\div\frac{8}{21}\)

    \(x+\frac{3}{5}=\frac{4}{7}\times\frac{21}{8}\)

    \(x+\frac{3}{5}=\frac{3}{2}\)

    \(x=\frac{3}{2}-\frac{3}{5}\)

    \(x=\frac{15}{10}-\frac{6}{10}\)

    \(x=\frac{9}{10}\)

Vậy x = \(\frac{9}{10}\)

2, Ta có :

    \(\frac{2}{3}+\frac{3}{4}\div x=-\frac{1}{6}\)

    \(\frac{3}{4}\div x=-\frac{1}{6}-\frac{2}{3}\)

    \(\frac{3}{4}\div x=-\frac{1}{6}-\frac{4}{6}\)

    \(\frac{3}{4}\div x=-\frac{5}{6}\)

    \(x=\frac{3}{4}\div\left(-\frac{5}{6}\right)\)

    \(x=\frac{3}{4}\times\left(-\frac{6}{5}\right)\)

    \(x=-\frac{9}{10}\)

Vậy x = \(-\frac{9}{10}\)

thanks bạn nha