a) 3/13 - 3/2 + 10/13

= (3/13 + 10/13) - 3/2

= 1 - 3/2

= -1/2

b) 4/7 - (-2/7) - 7/3

= 4/7 + 2/7 - 7/3

= 6/7 - 7/3

= -31/21

c) 2/3 - (-1/6) + 5/4

= 2/3 + 1/6 + 5/4

= 8/12 + 2/12 + 15/12

= 25/12

a, 3/13 - 3/2 + 10/13

= 3/13 + 10/13

= 1 - 3/2 = -1/2

b,4/7 - (-2/7) - 7/3

= 4/7 + 2/7 - 7/3

= 6/7 - 7/3

= 18/21 - 14/21

= 4/21

c, 2/3 - -1/6 +5/4 

= 2/3 + 1/16 +5/4

= 128/192 + 12/192 + 240/192

= 380/192

= 95/4 

không hiểu chỗ nào hỏi tui

trình bày ra hộ tôi

10 nha bạn chắcccccccccccccccc thế

:v bó tay ( chưa từng gặp dạng này )

Theo bài này ta tìm ra điểm chung:

(1)  (2)

4 = 6 

8 = 10

12 = 14

16 = ?

Ta thấy các số (1) kém các số (2)  là 2 đơn vị 

\(\Rightarrow\)16 = 18

\(\Rightarrow\)16 = 8 + 10 

Vậy 7 + 9 = 8 + 10 

\(A=\left(a\text{x}7+a\text{x}8-a\text{x}15\right):\left(1+2+3+...+10\right)\)

\(A=\left(a\text{x}\left(7+8-15\right)\right):\left(1+2+3+...+10\right)\)

\(A=\left(a\text{x}0\right):\left(1+2+3+..+10\right)\)

\(A=0:\left(1+2+3+...+10\right)\)

\(A=0\)

\(B=\left(18-9\text{x}2\right)\text{x}\left(2+4+6+8+10\right)\)

\(B=\left(18-18\right)\text{x}\left(2+4+6+8+10\right)\)

\(B=0\text{x}\left(2+4+6+8+10\right)\)

\(B=0\)

Câu trả lời B=0

1+2+3+4+5+6+7+8x9+10

$$[13 + 2(x-5)] \div 7 = 9$$

$$\iff 13 + 2(x-5) = 9 \times 7$$

$$\iff 13 + 2(x-5) = 63$$

$$\iff 2(x-5) = 63 - 13$$

$$\iff 2(x-5) = 50$$

$$\iff x-5 = 50 \div 2$$

$$\iff x-5 = 25$$

$$\iff x =25 + 5$$

$$\iff x = 30$$

\(12\frac{14}{25}\cdot6\frac{10}{12}=12\frac{14}{25}\cdot6\frac{5}{6}=\frac{314}{25}\cdot\frac{41}{6}=\frac{314\cdot41}{25\cdot6}=\frac{157\cdot2\cdot41}{25\cdot3\cdot2}=\frac{6437}{75}\)

\(5\frac{6}{9}\div7\frac{6}{3}=ERROR\)

\(12\frac{14}{25}x25\frac{10}{12}=\frac{314}{25}x\frac{310}{12}=\frac{97340}{300}=\frac{4867}{15}\)

\(5\frac{6}{9}:7\frac{6}{3}=\frac{51}{9}:\frac{27}{3}=\frac{51}{9}x\frac{3}{27}=\frac{153}{243}=\frac{17}{27}\)

\(\frac{6}{1.3}+\frac{6}{3.5}+\frac{6}{5.7}+...+\frac{6}{49.51}\)

\(=3\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{49.51}\right)\)

\(=3\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{49}-\frac{1}{51}\right)\)

\(=3\left(1-\frac{1}{51}\right)\)

\(=3.\frac{50}{51}\)

Chúc bn hok tốt

\(\frac{6}{1\cdot3}+\frac{6}{3\cdot5}+\frac{6}{5\cdot7}+...+\frac{6}{49\cdot51}\)

\(=3\left(\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+...+\frac{2}{49\cdot51}\right)\)

\(=3\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{49}-\frac{1}{51}\right)\)

\(=3\left(1-\frac{1}{51}\right)\)

\(=3\cdot\frac{50}{51}\)

\(=\frac{50}{17}\)

Đặt \(A=\frac{6}{1.3}+\frac{6}{3.5}+\frac{6}{5.7}+.........+\frac{6}{49.51}\)

\(A=\frac{6}{1.3}+\frac{6}{3.5}+\frac{6}{5.7}+........+\frac{6}{49.51}\)

\(=6\left(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+..........+\frac{1}{49.51}\right)\)

\(=\left(6.\frac{1}{2}\right)\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+........+\frac{2}{49.51}\right)\)

\(=3\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-........-\frac{1}{51}\right)\)

\(=3\left(1-\frac{1}{51}\right)\)

\(=3\left(\frac{51}{51}-\frac{1}{51}\right)\)

\(=3.\frac{50}{51}\)

\(=\frac{150}{51}\)

Vậy \(A=\frac{150}{51}\)

4-7+10-13+16-.....-2011+2014 6 tháng 2 2017 lúc 12:18
Ta có số cặp là:335 cặp và dư số 2014
Mà khoảng cách giữa 2 số liền nhau là:4-7=-3
Vậy 4-7+10-13+16-....-2011+2014 là:
335.(-3)+2014=1009

bn nên sửa đề bài là : Tính nhanh: 4-7+10-13+16-...-2011+2014

B= 1-4+7-10+........+2011-2014+2017 ( 673 số )

B = - 3 + ( - 3 ) + ........... + ( - 3 ) + 2017 ( 336 số -3 )

B = - 3 . 336 + 2017

B = - 1008 + 2017

B = 1009