1 C

2 A

3 A

4 B

5 D

6 B

7 D

8 D

9 C

10 C

11 D

12 B  

giúp mik vs ak mik mới vào học

đây là bài phần gạch chân phát âm khác nhau bạn ghi phần gạch chân vô nha r mk làm cho

`a) ((-14).15)/(21.(-10))`

`=(-7.3.5.3)/(7.3.(-2).5)`

`=3/2`

`b) ((-7).12)/((-16).(-14))`

`=(-7.3.2.2)/(-2.2.2.(-7).2)`

`=(-3)/4`

`c) ((-11).(-5))/(15.22) `

`=(-11.(-5))/(3.5.11.2)`

`=1/6`

`d) ((-10).(-18))/((-6).25.7)`

`=(-5.2.-2.3.3)/(-2.3.5.5.7)`

`=6/35`

`e) (5.7-7.9)/(7.2+6.7)`

`=(7.(5-9))/(7.(2+6))`

`=-4/8`

`=-1/2`

`f) (11.9-22.3)/(33.2)`

`=(33.(3-2))/(33.2)`

`=1/2`

Dấu này * là dấu nhân

Một năm rồi không có ai trả lời à 

THấy cx thương nhưng mk nhìn cái đề thì dài thật cx khó có ai có thời gian mà giải

Bài 1:

a. $(-20)+x=-30$

$x-20=-30$

$x=-30+20=-(30-20)=-10$

b.

$(-10)-x=-20$

$x=(-10)-(-20)=-10+20=20-10=10$

c. Đề sai. Bạn xem lại.

d.

$x+(-3)=-7$

$x=-7-(-3)=-7+3=-(7-3)=-4$

e.

$x-(-5)=-9$

$x=(-9)+(-5)=-14$

f.

$x(-11)=12$

$x=\frac{12}{-11}=\frac{-12}{11}$

h.

$2x-10=20$

$2x=20+10=30$

$x=30:2=15$

l.

$4x-8=-8$
$4x=-8+8=0$

$x=0:4=0$

k.

$-12-(-2)x=-8$

$(-2)x=-12-(-8)=-12+8=-(12-8)=-4$

$x=(-4):(-2)=2$

Bài 2:

a. $-20-(10-x)=-3$

$10-x=-20-(-3)=-20+3=-(20-3)=-17$

$x=10-(-17)=10+17=27$

b.

$14+(14-x)=-2$
$14-x=-2-14=-16$

$x=14-(-16)=14+16=30$

c.

$-15-(x-3)=-7$

$x-3=-15-(-7)=-15+7=-8$

x=-8+3=-5$

d.

$(x+4)+(-20)=-8$

$x+4=-8-(-20)=-8+20=12$
$x=12-4=8$

e.

$-2x-2=-4$

$-2x=-4+2=-2$

$x=(-2):(-2)=1$

f.

$-2x+4=-4$

$-2x=-4-4=-8$

$x=(-8):(-2)=4$

l.

$-12-(-2)x=-2-4=-6$

$(-2)x=-12-(-6)=-12+6=-6$

$x=(-6):(-2)=3$

Đề trên lỗi nhé ae , đề đúng đây:

1. Tìm số đối của mỗi số nguyên sau: -7; 0; -4; 12; |-5|
và |5|.
2. Tính:
a) 8274 + 226 ;
b) (- 5 ) + ( -11) ; c) (- 43) + (-9)
3. Tính:
a) 17 + ( - 7) ;
b) (-96) + 64 ;
c) 75 + ( -325)
4. Tính:
a) 10- (-3) ;
b) (-21) – (-19);
c) 13 – 30 ;
d) 9 – (- 9)
5. Tính tổng:
a) (-30) + 15 + 10 + ( -15) ;
b) 17 + ( -12) + 25 – 17 ; b) 17 + ( -12) + 25 – 17 ;
c) (-14) + 250 + ( - 16) + (- 250) ;
d) ( -3) + ( - 14) + 27 + ( -10)

1. số đối: -7; 0; -4; 12; \(|-5|\); 5

là: 7; 0; 4; -12; -5; -5

2,3,4,a, 8274 + 226 = 8500

b, -5 + -11 = -16

c, -43 + -9 = -52

d, 17 + -7 = 10

e, -96 + 64 = -32

f, 75 + -325 = -250

g, 10 - (-3) = 10 + 3 = 13

h, -21 + 19 = -2

.., 13 - 30 = -17

.., 9 + 9 = 18

5, a,

-30 + 15 + 10 + -15 = -30 + 10 = 20

b, 17 + -12 + 25 - 17 = -12 + 25 = 13

c,-14 +250 - 16 - 250 = -14 + -16 = -30

d,-3 - 14 + 27 - 10 = 0

e, -14 + 250 - 16 - 250 = -14 + -16 = -30

f, -3 - 14 + 27 - 10 = 0

Tính nhanh

a) 100 :4 – 50 : 2 + 100

 = 25 – 25 + 100

 = 0 + 100

 = 100

b) (6 × 8 – 48) : (10 + 11 + 12 + 13 + 14)

 = (48 – 48) : (10 + 11 + 12 + 13 + 14)

 = 0 : (10 + 11 + 12 + 13 + 14)

 = 0

c) 10000 × 2 + 60000

 = 10000 × 2 + 10000 × 6

 = 10000 × (2 + 6)

 = 10000 × 8

 = 80000

d) (7000 – 3000) × 2 = 4000 × 2 = 8000

a) (-12).10+9.10 = 10.[(-12)+9] = 10.(-3) = -30

b) (-11).8-(-11).9 = (-11).(8-9) = (-11).(-1) = 11

c) (-5).(-4) + (-5).14 = (-5).[(-4)+14] = -5.10 = -50

d) 13.(-3) + 13.8 = 13.[(-3)+8] = 13.5 = 65

a) = 1/10 - 1/11 + 1/11 -1/12 + 1/12 - 1/13 +1/13 1/14 +...+ 1/78 - 1/79

= 1/10 - 1/79

= máy tính ok

mấy câu khác bn làm tương tự là đc nhưng nhớ nhanh thêm khoảng cách giữa các mẫu nha

a)\(\frac{1}{10.11}+\frac{1}{11.12}+...+\frac{1}{78.79}=\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+...+\frac{1}{78}-\frac{1}{79}=\frac{1}{10}-\frac{1}{79}=\frac{69}{790}\)

b) \(\frac{8}{7.9}+\frac{8}{9.11}+...+\frac{8}{133.135}=4\left(\frac{2}{7.9}+\frac{2}{9.11}+...+\frac{2}{133.135}\right)\)

\(=4\left(\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{133}-\frac{1}{135}\right)=4\left(\frac{1}{7}-\frac{1}{135}\right)=4.\frac{128}{945}=\frac{456}{945}\)

c) \(\frac{12}{8.11}+\frac{12}{11.14}+...+\frac{12}{503.506}=4\left(\frac{3}{8.11}+\frac{3}{11.14}+...+\frac{3}{503.506}\right)\)

\(=4\left(\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+...+\frac{1}{503}-\frac{1}{506}\right)=4\left(\frac{1}{8}-\frac{1}{506}\right)=\frac{249}{506}\)

d) \(\frac{1}{4.7}+\frac{1}{7.10}+...+\frac{1}{391.394}=\frac{1}{3}\left(\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{391.394}\right)\)

\(=\frac{1}{3}\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{391}-\frac{1}{394}\right)=\frac{1}{3}.\left(\frac{1}{4}-\frac{1}{394}\right)=\frac{1}{3}.\frac{195}{788}=\frac{65}{788}\)

e) \(\frac{4}{5.8}+\frac{4}{8.11}+...+\frac{4}{602.605}=\frac{4}{3}.\left(\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{602.605}\right)\)

\(=\frac{4}{3}\left(\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{602}-\frac{1}{605}\right)=\frac{4}{3}\left(\frac{1}{5}-\frac{1}{605}\right)=\frac{4}{3}.\frac{24}{121}=\frac{32}{121}\)

g) Sửa đề\(1+\frac{1}{3}+\frac{1}{6}+...+\frac{1}{820}=2\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{1640}\right)=2\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{40.41}\right)\)

\(=2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{40}-\frac{1}{41}\right)=2\left(1-\frac{1}{41}\right)=2.\frac{40}{41}=\frac{80}{41}\)

Bài làm:

a) \(\frac{1}{10.11}+\frac{1}{11.12}+...+\frac{1}{78.79}\)

\(=\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+...+\frac{1}{78}-\frac{1}{79}\)

\(=\frac{1}{10}-\frac{1}{79}=\frac{69}{790}\)

b) \(\frac{8}{7.9}+\frac{8}{9.11}+...+\frac{8}{133.135}\)

\(=4\left(\frac{2}{7.9}+\frac{2}{9.11}+...+\frac{2}{133.135}\right)\)

\(=4\left(\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{133}-\frac{1}{135}\right)\)

\(=4\left(\frac{1}{7}-\frac{1}{135}\right)\)

\(=4.\frac{128}{945}=\frac{512}{945}\)

c) \(\frac{12}{8.11}+\frac{12}{11.14}+...+\frac{12}{503.506}\)

\(=4\left(\frac{3}{8.11}+\frac{3}{11.14}+...+\frac{3}{503.506}\right)\)

\(=4\left(\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+...+\frac{1}{503}-\frac{1}{506}\right)\)

\(=4\left(\frac{1}{8}-\frac{1}{506}\right)\)

\(=4.\frac{249}{2024}=\frac{249}{506}\)

d) \(\frac{1}{4.7}+\frac{1}{7.10}+...+\frac{1}{391.394}\)

\(=\frac{1}{3}\left(\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{391.394}\right)\)

\(=\frac{1}{3}\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{391}-\frac{1}{394}\right)\)

\(=\frac{1}{3}\left(\frac{1}{4}-\frac{1}{394}\right)\)

\(=\frac{1}{3}.\frac{195}{788}=\frac{65}{788}\)

e) \(\frac{4}{5.8}+\frac{4}{8.11}+...+\frac{4}{602.605}\)

\(=\frac{4}{3}\left(\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{602.605}\right)\)

\(=\frac{4}{3}\left(\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{602}-\frac{1}{605}\right)\)

\(=\frac{4}{3}\left(\frac{1}{5}-\frac{1}{605}\right)\)

\(=\frac{4}{3}.\frac{24}{121}=\frac{32}{121}\)

g) Phải sửa \(\frac{1}{802}\)  thành \(\frac{1}{820}\) nhé

\(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{820}\)

\(=1+\frac{1}{1.3}+\frac{1}{2.3}+\frac{1}{2.5}+...+\frac{1}{41.20}\)

\(=2\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{40.41}\right)\)

\(=2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{40}-\frac{1}{41}\right)\)

\(=2\left(1-\frac{1}{41}\right)\)

\(=2.\frac{40}{41}=\frac{80}{41}\)

a)-13-10-8-12

=-(13+10+8+12)=>-43

b)-14-7-12-21

=-(14+7+12+21)=>-54

c)-5-9-11-24

=-(5+9+11+24)=>-49

d)-6-8-13-17

=-(6+8+13+17)=>-44

e)-10-14-16-15

=-(10+14+16+15)=>-55

g)-3-7-25-45

=-(3+7+25+45)=>-80

tick cho mk nha bạn

a) = - (13 + 10 + 8 + 12) = - 43 

a)-13-10-8-12

=-(13+10+8+12)=>-43

b)-14-7-12-21

=-(14+7+12+21)=>-54

c)-5-9-11-24

=-(5+9+11+24)=>-49

d)-6-8-13-17

=-(6+8+13+17)=>-44

e)-10-14-16-15

=-(10+14+16+15)=>-55

g)-3-7-25-45

=-(3+7+25+45)=>-80

B

B