c) Ta có: \(\dfrac{3}{5}+\dfrac{-5}{20}+\dfrac{30}{75}+\dfrac{-7}{4}\)

\(=\dfrac{3}{5}+\dfrac{2}{5}+\dfrac{-1}{4}+\dfrac{-7}{4}\)

\(=1-2=-1\)

Giải:

a)-1/12+4/3=-1/12+16/12=15/12=5/4

b)(-4/14-3/15)-(1/5-20/35-(-1)).7

=-17/35-22/35.7

=-17/35-22/5

=-171/35

c)3/5+-5/20+30/75+-7/4

=3/5+-1/4+2/5+-7/4

=(3/5+2/5)+(-1/4+-7/4)

=1+-2

=-1

d)5/6.-12/14+7/13

=-5/7+7/13

=-16/91

e)2/-9-5/-36-1/4

=-1/12-1/4

=-1/3

f)2/23+-5/12+7/18+21/23+-7/12

=(2/23+21/23)+(-5/12+-7/12)+7/18

=1+-1+7/18

=7/18

a) 31 . { 330 : [178 – 4 . ( 35 – 21 : 3 )]} = 31 . { 330 : [178 – 4 . ( 35 – 7)]}

= 31 . { 330 : [178 – 4 . 28]} = 31 . { 330 : [178 – 112]}

= 31 . { 330 : 66 } = 31 . 5 = 155

b) ( 5 19  .  5 14 ) :  5 32  =  5 33 :  5 32 = 5

a) 31 . { 330 : [178 – 4 . ( 35 – 21 : 3 )]} = 31 . { 330 : [178 – 4 . ( 35 – 7)]}

= 31 . { 330 : [178 – 4 . 28]} = 31 . { 330 : [178 – 112]}

= 31 . { 330 : 66 } = 31 . 5 = 155

( 5 19 .  5 14 ) :  5 32 =  5 33 :  5 32  = 5

a. ( 23 - 21) + ( 19 - 17) + ( 15 - 13) + ( 11 - 9) + ( 7 - 5) + ( 3 - 1) 

= 2 + 2 + 2 + 2 + 2 + 2 

= 2 x 6

= 12

b. ( 24 - 22 ) + ( 20 - 18 ) + ( 16 - 14 ) + ( 12 - 10) + ( 8 - 6 ) + ( 4 - 2) 

= 2 + 2 + 2 + 2 + 2 + 2 

= 2 x 6 

= 12

Bài 1

S₂ = 21 + 23 + 25 + ... + 1001

Số số hạng của S₂:

(1001 - 21) : 2 + 1 = 491

⇒ S₂  = (1001 + 21) . 491 : 2 = 250901

--------

S₄  = 15 + 25 + 35 + ... + 115

Số số hạng của S₄:

(115 - 15) : 10 + 1 = 11

⇒ S₄ = (115 + 15) . 11 : 2 = 715

Bài 2

a) 2x - 138 = 2³.3²

2x - 138 = 8.9

2x - 138 = 72

2x = 72 + 138

2x = 210

x = 210 : 2

x = 105

b) 5.(x + 35) = 515

x + 35 = 515 : 5

x + 35 = 103

x = 103 - 35

x = 78

c) 814 - (x - 305) = 712

x - 305 = 814 - 712

x - 305 = 102

x = 102 + 305

x = 407

d) 20 - [7.(x - 3) + 4] = 2

7(x - 3) + 4 = 20 - 2

7(x - 3) + 4 = 18

7(x - 3) = 18 - 4

7(x - 3) = 14

x - 3 = 14 : 7

x - 3 = 2

x = 2 + 3

x = 5

e) 9ˣ⁻¹ = 9

x - 1 = 1

x = 1 + 1

x = 2

2:

a: \(2x-138=2^3\cdot3^2\)

=>\(2x-138=8\cdot9=72\)

=>2x=138+72=210

=>x=105

b: \(5\cdot\left(x+35\right)=515\)

=>x+35=103

=>x=103-35=68

c: \(814-\left(x-305\right)=712\)

=>x-305=814-712=102

=>x=102+305=407

d: \(20-\left[7\left(x-3\right)+4\right]=2\)

=>7(x-3)+4=18

=>7(x-3)=14

=>x-3=2

=>x=5

e: \(9^{x-1}=9\)

=>x-1=1

=>x=2

f: \(5^{x-2}-3^2=2^4-\left(2^8\cdot2^2-2^{10}\cdot2^2\right)\)

=>\(5^{x-2}-9=16-1024+4096\)

=>\(5^{x-2}=3097\)

=>\(x-2=log_53097\)

=>\(x=2+log_53097\)

a) 463+318+137+22

 = (463+137)+(318+22)

 =  600+340

 = 940

b) 185.32-32.85

 =  32.(185-85)

 =  32 . 100

 =  3200

c) \(15:\left\{390:\left[500-\left(125+35.7\right)\right]\right\}\)

\(\text{= }15:\left\{390:\left[500-\left(125+245\right)\right]\right\}\)

\(\text{= }15:\left\{390:\left[500-370\right]\right\}\)

\(=15:\left(390:130\right)\)

\(\text{= }15:3\)

\(\text{= }5\)

a)\(463+318+137+22\)

\(=\left(463+137\right)+\left(318+22\right)\)

\(=600+340=940\)

b)\(185.3^2-3^2.85\)

\(=3^2.\left(185-85\right)\)

\(=9.100=900\)

c)\(15:\left\{390:\left[500-\left(125+35.7\right)\right]\right\}\)

\(=15:\left\{390:\left[500-\left(125+245\right)\right]\right\}\)

\(=15:\left\{390:\left[500-370\right]\right\}\)

\(=15:\left\{390:130\right\}\)

\(=15:3=5\)

a) 463 + 318 + 137 + 22 = (463 + 137) + (318 +22) = 600 + 340 = 940

a) (26-6)*(-4)+31*(-7-13)

=-80+-620

=-700

hacker 2k6