1 Tìm số nguyên x bik:

a.-( 2x+2)+25=-19           

-2x - 2 + 25 = - 19

-2x = -19+2-25

-2x = -42

   x = 21   

 b.1-(12+3x)=7

1 - 12 - 3x = 7

- 11 - 3x = 7

 -3x = 7 + 11

- 3x = 18

    x = -6

c.-(2x+2)+25=-19

 giống câu a nhé

2.Rút gọn biểu thức 

a.2x+(-61)-(21-61)       

= 2x - 61 - 21 + 61

= 2x - 21  

b. (-3-x+5)+3

= 2 - x + 3

= -1 -x 

c.11-(13-x)+(13-11)         

= 11 - 13 + x + 13 - 11

= x

d.25-(15-x+303)+303

= 25 - 15 + x - 303 + 303

= 10 + x

e.x+(-81)-(11-8)                     

= x - 81 - 11 + 8

= x - 84

f. (-1-x+2)+1

= -1 - x + 2 + 1

= - x + 2

g.15-(11-x)+(11-15)             

= 15 - 11 + x + 11 - 15

= x  

i) 15-(15-x+202)+202

= 15 - 15 + x - 202 + 202

= x

3.Chứng minh đẳng thức

a.-(59-3x)+39=3x-20       

- 59 + 3x + 39 = 3x - 20

- 59 + 39 + 20 = 3x - 3x

           0          = 0

b.-(a+b+c)+(b-c)-(a-c-1)=1+c-29

b - a - b - c + b - c - a + c + 1 = 1 + c - 29

b - a - b - c + b - c - a + c - c = 1 - 29 - 1

                   - 2a + b - 2c          = - 29

chịu luôn  -__- 

c.-(19-2x)+39=2x+20

- 19 + 2x + 39 = 2x + 20

2x - 2x = 20 + 19 - 29

0          = 0

d.-(a+b+c)+b-c-( a-c+1)=c-2a-1

- a - b - c + b - c - a + c - 1 = c - 2a - 1

- a - b - c + b - c - a + c + 2a - c = -1 + 1

                     - 2c  =  0

                         c  = 0

Vậy c = 0

Tương tự 5. HS tự làm

ccc ngô ngọc thảo vy - 4B

Áp dụng quy tắc dấu ngoặc rồi thực hiện các phép tính, ta thu được kết quả.a)   x + 71. b) 3 - x. c) x + 23. d) 23 - x

25 - ( 15 - x + 303) + 303 = 25 - 15 + (303 - 303) + x = x + 10

a ) 2x + (-61)-(21-61)

= 2x - 61 - 21 + 61

= 2x - 21

b) (-3-x+5) +3

= -3 - x + 5 + 3

= -x + 5

a) 2x + (-61) -21+61

= 2x - 21

b) (-3-x+5) +3

= -3+3-x+5

= -x+5

a) \(2x+\left(-61\right)-\left(21-61\right)\)

\(=2x-61-\left(-40\right)\)

\(=2x-61+40\)

\(=2x+\left(-61+40\right)\)

\(=2x-21\)

b) \(\left(-3-x+5\right)+3\)

\(=2-x+3\)

\(=-x+\left(2+3\right)\)

\(=5-x\)

\(a.A=\left(x-2\right)^2+\left(y+1\right)^2+1\ge1\forall x;y\) . " = " \(\Leftrightarrow x=2;y=-1\) 

b.\(B=7-\left(x+3\right)^2\le7\forall x\)  " = " \(\Leftrightarrow x=-3\)

c.\(C=\left|2x-3\right|-13\ge-13\forall x\)  " = " \(\Leftrightarrow x=\dfrac{3}{2}\)

d.\(D=11-\left|2x-13\right|\le11\forall x\)  " = " \(\Leftrightarrow x=\dfrac{13}{2}\)

a) \(x+5=20-\left(12-7\right)\)

\(\Rightarrow x+5=20-5\)

\(\Rightarrow x+5=15\)

\(\Rightarrow x=15-5\)

\(\Rightarrow x=10\)

b) \(15-\left(3+2x\right)=2^2\)

\(\Rightarrow3+2x=15-4\)

\(\Rightarrow3+2x=11\)

\(\Rightarrow2x=11-3\)

\(\Rightarrow2x=8\)

\(\Rightarrow x=\dfrac{8}{2}\)

\(\Rightarrow x=4\)

c) \(-11-\left(19-x\right)=50\)

\(\Rightarrow19-x=-11-50\)

\(\Rightarrow19-x=-61\)

\(\Rightarrow x=61+19\)

\(\Rightarrow x=80\)

d) \(159-\left(25-x\right)=43\)

\(\Rightarrow25-x=159-43\)

\(\Rightarrow25-x=116\)

\(\Rightarrow x=25-116\)

\(\Rightarrow x=-91\)

e) \(\left(79-x\right)-43=-\left(17-52\right)\)

\(\Rightarrow\left(79-x\right)-43=52-17\)

\(\Rightarrow79-x-43=35\)

\(\Rightarrow36-x=35\)

\(\Rightarrow x=1\)

f) \(\left(7+x\right)-\left(21-13\right)=32\)

\(\Rightarrow7+x-8=32\)

\(\Rightarrow x-1=32\)

\(\Rightarrow x=32+1\)

\(\Rightarrow x=33\)

g) \(-x+20=-15+8+13\)

\(\Rightarrow-x+20=6\)

\(\Rightarrow x=20-6\)

\(\Rightarrow x=14\)

h) \(-\left(-x+13-142\right)+18=55\)

\(\Rightarrow x-13+142+18=55\)

\(\Rightarrow x+147=55\)

\(\Rightarrow x=55-147\)

\(\Rightarrow x=-92\)