=87.(-17+(-83)=87.(-100)=-8700

=-45.(1+432-432)=-45.1=-45

a, =87[-17+(-83)]

=87.(-100)

=-8700

b, =(-45)+-(45).432-432.(-45)

(-45)+(-45)(432-432)

=(-45)+0

=-45

tính hợp lý
87 x (- 17) + (- 83) x 87

= 87.[-17+(-83)]

=87.(-100)

=-8700
(- 45) x (1 + 432) - 432 x (- 45)

=-45.433-432.(-45)

=-45.(433-432)

=-45.1

=-45

a: \(=\dfrac{18}{51}\cdot\dfrac{34}{9}\cdot\dfrac{17}{18}=\dfrac{17}{51}\cdot\dfrac{34}{9}=\dfrac{1}{3}\cdot\dfrac{34}{9}=\dfrac{34}{27}\)

b: \(=\dfrac{21}{32}\cdot\dfrac{4}{7}\cdot25\cdot\dfrac{4}{5}=\dfrac{21}{7}\cdot\dfrac{4}{32}\cdot20=60\cdot\dfrac{1}{8}=\dfrac{15}{2}\)

1. Thực hiện phép tính bằng cách hợp lí :

a) (-46) + (-125) + 46 + 25 = [(-46)+46] + [(-125)+25]

= 0+(-100) = -100

b) 25.(-15) + 25.(-5) + (-20).75 = 25.[(-15)+(-5)] + (-20).75

= 25.(-20) + (-20).75 = (-20).(25+75) = (-20).100 = -2000

c) (-151)+(-37)+(-42)+(-63)+142 =(-151)+[(-37)+(-63)]+[(-42)+142]

= (-151) + [(-100) + 100] = -151

d)32+(-149)+(-311)+(-89)+(-51) = 32+[(-149)+(-51)] + [(-311)+(-89)]

= 32+[(-200)+(-400)] = 32+(-600) = -568

e)-65.(87-17)-87.(17-65) = (-65).87 - (-65).17 - 87.17 + 87.65

= (-65).87 + 65.17 - 87.17 + 87.65 = [(-65).87+87.65] + 65.(17-87)

= 65.(-70) = -4550

g) -43.(53-16) - 53.(16-43) = (-43).53 - (-43).16 - 53.16 + 53.43

= (-43).53 + 43.16 - 53.16 + 53.43 = [(-43).53+53.43] + 16.(43-53)

= 16.(-10) = -160

2: \(=\dfrac{-2}{75}+\dfrac{5}{39}=\dfrac{33}{325}\)

3: \(=\dfrac{6}{11}\left(\dfrac{4}{9}+\dfrac{5}{9}\right)=\dfrac{6}{11}\)

4: \(=\dfrac{7}{19}\left(\dfrac{5}{13}+\dfrac{8}{13}-1\right)=-2\cdot\dfrac{7}{19}=-\dfrac{14}{19}\)

5: \(=\dfrac{2}{7}\left(\dfrac{4}{23}-\dfrac{27}{23}+1\right)=0\)

6: \(=\dfrac{3}{8}\left(\dfrac{3}{7}+\dfrac{4}{7}\right)+\dfrac{11}{8}=\dfrac{3}{8}+\dfrac{11}{8}=\dfrac{14}{8}=\dfrac{7}{4}\)

1.4./x-5/-54=-34

4./x-5/=-34+54

4./x-5/=20

/x-5/=20:4

/x-5/=5

=>x-5=5 va x-5=-5

TH1:x-5=-5

=>x=0

TH2:x-5=5

=>x=10

2. /x-1/+(-5)=2

/x-1/=2-(-5)

/x-1/=7

=>x-1=7 va x-1=-7

TH1: x-1=7

=>x=8

TH2:x-1=-7

=>x=-6

vay x=-6 hoac x=8

3. 32-8./2x-9/=24

8./2x-9/=32-24=8

/2x-9/=8:8=1

=>2x-9=1 hoac 2x-9=-1

TH1: 2x-9=1

=>x=(1+9):2=5

TH2: 2X-9=-1

=>x=(-1+9):2=4

vay x=4 hoac x=5

LƯỜI QUEN THÂN MẤT NẾT

mọi người giúp bn ấy đê

mk lười gõ

mk lười tính

mk lười lắm

lười thì chết thôi

ko ai rảnh tay trả lời đâu

tự túc là hạnh phúc bn ạ

^_^

2a) (a + 2b - c) - (3a - 4b + 5c) - 8c

= a + 2b - c - 3a + 4b - 5c - 8c

= (a - 3a) + (2b + 4b) - (c + 5c + 8c)

= -2a + 6b - 14c

b) (a - 3b + 4) - (5a + 6b - 7) - 8

= a - 3b + 4 - 5a - 6b + 7 - 8

= (a - 5a) - (3b + 6b) + (4 + 7 - 8)

= -4a - 9b + 3

1. \(x-8+32=68\)

\(x-8=68-32\)

\(x-8=36\)

\(x=36+8\)

\(x=44\)

_____

2. \(x+8+32=68\)

\(x+8=68-32\)

\(x+8=36\)

\(x=36-8\)

\(x=28\)

_____

3. \(98-x+34=43\)

\(98-x=43-34\)

\(98-x=9\)

\(x=98-9\)

\(x=89\)

_____

4. \(98+x-34=43\)

\(98+x=43+34\)

\(98+x=77\)

\(x=77-98\)

\(x=-21\)

_____

5. \(x:5:4=800\)

\(x:5=800.4\)

\(x:5=3200\)

\(x=3200.5\)

\(x=16000\)

_____

6. \(18+x=384:8\)

\(18+x=48\)

\(x=48-18\)

\(x=30\)

_____

7. \(\left(84,6-2\times x\right):3,02=5,1\)

\(84,6-2.x=5,1.3,02\)

\(84,6-2.x=15,402\)

\(2.x=84,6-15,402\)

\(2.x=69,198\)

\(x=69,198:2\)

\(x=34,599\)

_____

8. \(x\times5=120:6\)

\(x.5=20\)

\(x=20:5\)

\(x=4\)

_____

9. \(\left(15\times24-x\right):0,25=100:0,25\)

\(\left(15.24-x\right):0,25=400\)

\(15.24-x=400.0,25\)

\(15.24-x=100\)

\(360-x=100\)

\(x=360-100\)

\(x=260\)

1,x-8+32=68

=>x-8=68-32=36

=>x=36+8=42

2,x+8+32=68

=>x+8=68-32=36

=>x=36-8=28

3,98-x+34=43

=>98-x=43-34=9

=>x=98-9=89

4,98+x-34=43

=>98+x=43+34=77

=>x=77-98=-21

5,x:5:4=800

=>x:20=800

=>x=800x20=16000

6,18+x=384:8=48

=>x=48-18=30

7,(84,6-2x):3,02=5,1

=>84,6-2x=5,1x3,02=15,402

=>2x=84,6-15,402=69,198

=>x=69,198:2=34,599

8,5x=120:6=20

=>x=20:5=4

9,(15x24-x):0,25=100:0,25=400

=>360-x=400x0,25=100

=>x=360-100=260.

1. \(...\Rightarrow x+24=68\Rightarrow x=68-24=44\)

2. \(...\Rightarrow x+40=68\Rightarrow x=68-40=28\)

3. \(...\Rightarrow3^{2\left(8+x\right)}=9=3^2\Rightarrow2\left(8+x\right)=2\Rightarrow8+x=1\Rightarrow x=-7\)

4. \(...\Rightarrow3^{2\left(8+x\right)}=77\) (bạn xem lại đề)

5. \(...\Rightarrow x:5=800.4\Rightarrow x:5=3200\Rightarrow x=3200.5=16000\)

6. \(...\Rightarrow18+x=48\Rightarrow x=48-18=30\)

7. \(...\Rightarrow84,6-2x=5,1.3,02=15,402\Rightarrow2x=84,6-15,402\Rightarrow2x=69,198\Rightarrow x=34,599\)

8. \(...\Rightarrow5.x=20\Rightarrow x=20:5=4\)

9. \(\left(360-x\right):0,25=400\Rightarrow360-x=400.0,25=100\Rightarrow x=400-100=300\)

432/45 + 14.7 = 24.3

823.2 / 8.4 - 98 = 0

(754.4 + 333.1 ) / 12.5 = 87

\(\frac{432}{45}+x=24,3\)

\(\Leftrightarrow9,6+x=24,3\)

\(\Leftrightarrow x=24,3-9,6=14,7\)

\(823,2:84-x=0\)

\(\Leftrightarrow98-x=0\Leftrightarrow x=98\)

\(\frac{754,4+333,1}{x}=87\)

\(\Leftrightarrow754,4+333,1=87x\)

\(\Leftrightarrow1087,5=87x\)

\(\Rightarrow x=1087,5:87=12,5\)

=1087,5:x=87

=1087,5:87

=12,5