6 + 1 = 7     5 + 2 = 7     4 + 3 = 7

1 + 6 = 7     2 + 5 = 7     3 + 4 = 7

7 - 6 = 1     7 - 5 = 2     7 - 4 = 3

7 - 1 = 6     7 - 2 = 5     7 - 3 = 4

6+1=7

1+6=7

7-6=1

7-1=6

5+2=7

2+5=7

7-5=2

7-2=5

4+3=7

3+4=7

7-4=3

7-3=4

Lời giải chi tiết:

tách ra bn

khó nhìn quá:V

\(A=1+7+7^2+7^3+...+7^{2007}\)

\(7A=7+7^2+7^3+7^4+...+7^{2008}\)

\(7A-A=\left(7+7^2+7^3+7^4+...+7^{2008}\right)-\left(1+7+7^2+7^3+...+7^{2007}\right)\)

\(6A=7^{2008}-1\)

\(A=\frac{7^{2008}-1}{6}\)

Tương tự, \(B=\frac{4^{101}-1}{3},C=\frac{3^{101}-1}{2}\).

\(D=7+7^3+7^5+7^7+...+7^{99}\)

\(7^2.D=7^3+7^5+7^7+7^9+...+7^{101}\)

\(\left(7^2-1\right)D=\left(7^3+7^5+7^7+7^9+...+7^{101}\right)-\left(7+7^3+7^5+7^7+...+7^{99}\right)\)

\(48D=7^{101}-7\)

\(D=\frac{7^{101}-7}{48}\)

Tương tự, \(E=\frac{2^{9011}-2}{3}\)

a) Cách 1 : (3/4 + 1/2) x 5/7

               = 5/4 x 5/7

                = 25/28

Cách 2 : (3/4 + 1/2) x 5/7

           = 3/4 x 5/7 + 1/2 x 5/7

            = 15/28 + 5/14

            = 25/28

b) Cách 1 : 5/7 x 13/21 + 2/7 x 13/21

= 65/147 + 26/147

= 13/21

Cách 2 : 5/7 x 13/21 + 2/7 x 13/21

= (5/7 + 2/7) x 13/21

= 1 x 13/21

= 13/21

câu c tự làm

8 /15 :2/3+7/15:2/3 =                                              tính bằng 2 cách nhé các bạn

7 - 3 - 2 = 2     7 - 6 - 1 = 0     7 - 4 - 2 = 1

7 - 5 - 1 = 1     7 - 2 - 3 = 2     7 - 4 - 3 = 0

bạn viết cái này nó dễ hơn đó 

a: \(B=\frac12-\left\lbrack\frac38+\left(-\frac74\right)\right\rbrack\)

\(=\frac12-\frac38+\frac74\)

\(=\frac48-\frac38+\frac{14}{8}=\frac{15}{8}\)

b: \(-\frac{4}{12}-\left(-\frac{13}{39}-0,25\right)+0,75\)

\(=-\frac13+\frac13+0,25+0,75\)

=0,25+0,75

=1

c: \(\frac12-\frac13+\frac{1}{23}+\frac16\)

\(=\left(\frac12-\frac13+\frac16\right)+\frac{1}{23}\)

\(=\left(\frac16+\frac16\right)+\frac{1}{23}=\frac13+\frac{1}{23}=\frac{26}{69}\)

d: \(\left(-\frac{13}{7}-\frac49\right)-\left(-\frac{10}{7}-\frac49\right)\)

\(=-\frac{13}{7}-\frac49+\frac{10}{7}+\frac49\)

\(=-\frac{13}{7}+\frac{10}{7}=-\frac37\)

e: \(\left(\frac78-\frac52+\frac47\right)-\left(-\frac37+1-\frac{13}{8}\right)\)

\(=\frac78-\frac52+\frac47+\frac37-1+\frac{13}{8}\)

\(=\frac{20}{8}-\frac52=0\)

f: \(-\frac37+\left(3-\frac34\right)-\left(2,25-\frac{10}{7}\right)\)

\(=-\frac37+3-\frac34-2,25+\frac{10}{7}\)

\(=\frac77+0,75-\frac34\)

=1
g: \(\left(\frac53-\frac37+9\right)-\left(2+\frac57-\frac23\right)+\left(\frac87-\frac43-10\right)\)

\(=\frac53-\frac37+9-2-\frac57+\frac23+\frac87-\frac43-10\)

\(=\left(\frac53+\frac23-\frac43\right)+\left(-\frac37-\frac57+\frac87\right)+\left(9-2-10\right)\)

\(=\frac33+7-10=1-3=-2\)

giúp nhanh ạ, mình cần gấp

Bài 5:

a: =1/3+2/5

=5/15+6/15

=11/15

b: =6/21+12/21=18/21=6/7

c: =16/24+10/24

=26/24

=13/12

d: =4/12+3/12+10/12

=17/12

e: =19/24-9/24

=10/24

=5/12

f: =8/9-3/9=5/9

g: =9/3+1/3=10/3

k: =15/24+42/24+14/24

=71/24