15 - (-85) - (-70) + 15 + (-85)

<=> 15 + 85 + 70 + 15 + (-85)

<=> ( 15 + 15 ) + [ 85 + (-85) ] + 70

= 30 + 0 + 70

= 100

= 15 + 85 + 70 + 15 - 85

= ( 15 + 15 + 70 ) + ( 85 - 85 )

= 30 + 70 + 0

= 100

tick đi bạn

1)

a) -(2+5) = -2 - 5 = -7

b) +(-3+6) = -3 + 6 = 3

c) (-50+3) = -50 + 3 = -47

d) -(-2+3) = 2 - 3 = -1

e) -(10-3) = -10 + 3 = -7

f) -(-3)-(-3+1) = 3 + 3 - 1 = 5

g) (-5)+(-2+10) = -5 - 2 + 10 = 3

2)

a) -50+120+(-150)-20+30

= -(50 + 20) + (120 + 30 - 150)

= -70

b) 265-70+(-65)-30+15

= (265 - 65) - (70 + 30) + 15

= 200 - 100 + 15 = 115

c) -17+185-183+(-85)-63

= (185 - 85) - (183 + 17) - 63

= 100 - 200 - 63 = -163

d) -30+60+(-170)-260+19

= -(170 + 30) - (260 - 60) + 19

= -200 - 200 + 19 = -381

  50 + 55 + 60 + 65 + 70 + 75 + 80 + 85

= ( 50 + 85 ) + ( 55 + 80 ) + ( 60 + 75 ) + ( 65 + 70 ) ------ ( có 4 cặp số ) 

= 135 x 4 = 540 

Số các số hạng là (85 - 50)/5 + 1 = 8 (số)

Tổng trên là:

8 * (85 + 50) / 2 = 540 

Tui làm mà ko ai thèm tick luôn !!! Híc híc

Đáp án cần chọn là: A

Ta có 

90–85 +80–75+70–65+60–55+50–45

=5+5+5+5+5=10+10+5=25.

Đáp án  A

7)    \(\frac{x+25}{75}+\frac{x+30}{70}=\frac{x+35}{65}+\frac{x+40}{60}\)

\(\Leftrightarrow\)\(\frac{x+25}{75}+1+\frac{x+30}{70}+1=\frac{x+36}{65}+1+\frac{x+40}{60}+1\)

\(\Leftrightarrow\)\(\frac{x+100}{75}+\frac{x+100}{70}=\frac{x+100}{65}+\frac{x+100}{60}\)

\(\Leftrightarrow\)\(\left(x+100\right)\left(\frac{1}{75}+\frac{1}{70}-\frac{1}{65}-\frac{1}{60}\right)=0\)

\(\Leftrightarrow\)\(x+100=0\)            (vì 1/75 + 1/70 - 1/65 - 1/60  \(\ne\)0)

\(\Leftrightarrow\)\(x=-100\)

Vậy.....

7)    \(\frac{x+25}{75}+\frac{x+30}{70}=\frac{x+35}{65}+\frac{x+40}{60}\)

\(\Leftrightarrow\)\(\frac{x+25}{75}+1+\frac{x+30}{70}+1=\frac{x+35}{65}+1+\frac{x+40}{60}+1\)

\(\Leftrightarrow\)\(\frac{x+100}{75}+\frac{x+100}{70}=\frac{x+100}{65}+\frac{x+100}{60}\)

\(\Leftrightarrow\)\(\left(x+100\right)\left(\frac{1}{75}+\frac{1}{70}-\frac{1}{65}-\frac{1}{60}\right)=0\)

\(\Leftrightarrow\)\(x+100=0\)    (1/75 + 1/70 - 1/65 - 1/60 \(\ne\)0)

\(\Leftrightarrow\)\(x=-100\)

Vậy...

a) 65 . ( - 19 ) + 19 . ( - 24 )

= - 65 . 19 + 19 . ( - 24 )

= ( - 65 + - 24 ) . 19

= - 89 . 19

= - 1691

b ) 45 - 15 : 3

= 45 - 5

= 40

c ) 15 - ( - 85 ) - ( - 70 ) + 15 + ( - 85 )

= 15 + 85 + 70 + 15 + ( - 85 )

= 15 + 15 + 85 + ( - 85 ) + 70

= 30 + [ 85 + ( -85 ) ] + 70

= 30 + 0 + 70

= 30 + 70

= 100

d) 737737 . 255 - 255255 . 737

= 737 . 1001 . 255 - 255 . 1001 . 737

= ( 737 . 255 - 737 . 255 ) . 1001

= 0 . 1001

= 0

NHỚ K CHO MK NHA

a) = (-1235) + (-456)

   =-1691

b) 45 - 15:3

   = 45 - 5

   = 40

c) 15 - ( -85) - (-70) + 15 + (-85)

 = 15 + 15 - (-85) - 85 -( -70)

= 30 - 0 - (-70)

= 100

d) =737.1001. 255 - 255.1001.737

    = 0

Nhớ k cho mình nếu bạn thấy đúng nhé!

9: \(\dfrac{x-49}{50}+\dfrac{x-50}{49}=\dfrac{49}{x-50}+\dfrac{50}{x-49}\)

=>x-99=0

hay x=99

7: \(\Leftrightarrow\left(\dfrac{x+25}{75}+1\right)+\left(\dfrac{x+30}{70}+1\right)=\left(\dfrac{x+35}{65}+1\right)+\left(\dfrac{x+40}{60}+1\right)\)

=>x+100=0

hay x=-100

8:

Sửa đề: \(\dfrac{99-x}{101}+\dfrac{97-x}{103}+\dfrac{95-x}{105}+\dfrac{93-x}{107}=-4\) 

\(\Leftrightarrow\left(\dfrac{99-x}{101}+1\right)+\left(\dfrac{97-x}{103}+1\right)+\left(\dfrac{95-x}{105}+1\right)+\left(\dfrac{93-x}{107}+1\right)=0\)

=>200-x=0

hay x=200