a) 13.7 + 7.7

= (13 + 7).7

= 20 . 7

= 140

b) 2³ . 2016 . 5²

= 8 . 2016 . 25

= 200 . 2016

= 403200

c) 3² . 15 - 5.9

= 9.15 - 5.9

= (15 - 5).9

= 10.9

= 90

d) 13 + 15 + ........... + 57 + 59

Áp dụng công thức tính dãy số ta có :

\(\frac{\left[\left(59-13\right):2+1\right].\left(59+13\right)}{2}=\frac{24.72}{2}=864\)

a) 13 . 7 + 7 . 7

= (13 + 7) . 7

= 20 . 7

= 140

b) 2³ . 2016 . 5²

= 8 . 2016 . 25

= ( 8 . 25 ) . 2016

= 200 . 2016

= 403200 

c) 3² . 15 - 5 . 9

= 9 . 15 - 45

= 9 . 15 - 15 . 3

= ( 9 - 3 ) . 15

= 6 . 15

= 90

d) 13 + 15 + ........ + 57 + 59

Dãy số trên có số số hạng là:

( 59 - 13 ) : 2 + 1= 24 ( số hạng )

Tổng của dãy số trên là:

( 59 + 13 ) x 24 : 2 = 864

a, A = ( 1/3 + 12/67 + 13/41 ) - ( 79/67 - 28/41 )

A = (\(\frac13\) + \(\frac{12}{67}\) + \(\frac{13}{41}\)) - (\(\frac{79}{67}\) - \(\frac{28}{41}\))

A = \(\frac13\) + \(\frac{12}{67}\) + \(\frac{13}{41}\) - \(\frac{79}{67}\) + \(\frac{28}{41}\)

A = - (\(\frac{79}{67}-\frac{12}{67}\)) + (\(\frac{13}{41}\) + \(\frac{28}{41}\))

A = - 1 + 1 + \(\frac13\)

A = 0 + \(\frac13\)

A = \(\frac13\)

b, B = 3/4×7 + 3/7×10 + 3/10×13 + ......+ 3/73×76

B = \(\frac{3}{4\times7}\) + \(\frac{3}{7\times10}\) + \(\frac{3}{10\times13}\) + ... + \(\frac{3}{73\times76}\)

B = \(\frac14-\frac17\) + \(\frac17-\frac{1}{10}\) + ... + \(\frac{1}{73}-\frac{1}{76}\)

B = \(\frac14\) - \(\frac{1}{76}\)

B = \(\frac{19}{76}-\) \(\frac{1}{76}\)

B = \(\frac{18}{76}\)

B = \(\frac{9}{38}\)

`a: =(7/3-4/3)+11/5=16/5`

`b: =(18/13-5/13)+55/46=1+55/46=101/46`

`c: =27/25-4/9-2/25+5/9=(27/25-2/25)+(5/9-4/9)=1+1/9=10/9`

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cứ bình tĩnh bạn ơi

  13 - 12 + 11 - 10 - 9 + 8 - 7 - 6 + 5 - 4 + 3 + 2 - 1 
= ( 13 - 12 + 11 - 10 + 8 ) - ( 9 + 1 ) - ( 6 + 4) + ( 3 + 2 + 5 ) - 7 
= 10 - 10 - 10 + 10 - 7 
= ( 10 - 10 ) - ( 10 - 10 ) - 7 
= 0 - 0 - 7 
= - 7

\(13-12+11+10-9+8-7-6+5-4+3+2-1\)

\(=\left(13-12+11-10+8\right)-\left(9+1\right)-\left(6+4\right)+\left(3+2+5\right)-7\)

\(=10-10-10+10-7\)

\(=-7\)

a; - \(\dfrac{10}{13}\) + \(\dfrac{5}{17}\) - \(\dfrac{3}{13}\) + \(\dfrac{12}{17}\) - \(\dfrac{11}{20}\)

= - (\(\dfrac{10}{13}\) + \(\dfrac{3}{13}\)) + (\(\dfrac{5}{17}\) + \(\dfrac{12}{17}\)) - \(\dfrac{11}{20}\)

= - 1 + 1  - \(\dfrac{11}{20}\)

=   0 - \(\dfrac{11}{20}\)

= - \(\dfrac{11}{20}\)

b; \(\dfrac{3}{4}\) + \(\dfrac{-5}{6}\) - \(\dfrac{11}{-12}\)

= \(\dfrac{9}{12}\) - \(\dfrac{10}{12}\) + \(\dfrac{11}{12}\)

= \(\dfrac{10}{12}\)

= \(\dfrac{5}{6}\)

c; [13.\(\dfrac{4}{9}\) + 2.\(\dfrac{1}{9}\)] - 3.\(\dfrac{4}{9}\)

= [\(\dfrac{52}{9}\) + \(\dfrac{2}{9}\)] - \(\dfrac{4}{3}\)

= \(\dfrac{54}{9}\) - \(\dfrac{4}{3}\)

= \(\dfrac{14}{3}\)

Câu a:

A = 7 2/13 - (5 2/13 + 2 1/2)

A = 7 2/13 - 5 2/13 - 2 1/2

A = 2 - 2 1/2

A = 2 - 2 - 1/2

A = 0 - 1/2

A = -1/2

Câu b:

B = - 3/4 + 25% : (10 3/10 - 9 4/5) - (-1/2)^2

B = - 3/4 + 1/4 : (103/10 - 49/5) - 1/4

B = - 3/4 + 1/4 : (103/10 - 98/5) - 1/4

B = (-3/4 - 1/4) + 1/4 : (1/2)

B = -1 + 1/4 x 2/1

B = -1 + 1/2

B = - 1/2

Câu a:

A = 7 2/13 - (5 2/13 + 2 1/2)

A = 7 2/13 - 5 2/13 - 2 1/2

A = 2 - 2 1/2

A = 2 - 2 - 1/2

A = 0 - 1/2

A = -1/2

Câu b:

B = - 3/4 + 25% : (10 3/10 - 9 4/5) - (-1/2)^2

B = - 3/4 + 1/4 : (103/10 - 49/5) - 1/4

B = - 3/4 + 1/4 : (103/10 - 98/5) - 1/4

B = (-3/4 - 1/4) + 1/4 : (1/2)

B = -1 + 1/4 x 2/1

B = -1 + 1/2

B = - 1/2