Lời giải:
a. $=13-47-13-59+81+35-13$

$=(13-13-13)-(47+59)+(81+35)$
$=-13-106+116=-13+(116-106)=-13+10=-3$

b.

$=345-61+84+61-116-345$

$=(345-345)+(-61+61)-(116-84)$

$=0+0-32=-32$

a, $(13-47)-(13+59-81)+(35-13)$

$=13-47-13-59+81+35-13$

$=(13-13)+(-47-13)+(-59+81)+35$

$=-60+22+35$

$=-38+35$

$=-3$

$---$

b, $(345-61+84)-(-61+116+345)$

$=345-61+84+61-116-345$

$=(345-345)+(-61+61)+(84-116)$

$=-32$

   (10² + 11² + 12²) : (13² + 14²)

= (100 + 121 + 144) :( 169 + 196)

= 365: 365

= 1 

a) Suy ra : \(x\in BCNN\left(14,21\right)\)

14 = 2.7

21 = 3.7

=> BCNN (14,21)=7.2.3=42

Vậy x = 42

b) 200-(2x+6)=4^3

=>200-2x-6=64

=>194-2x=64

=>2x=194-64=130

=>x=65

a) x ⋮ 14 và x ⋮ 21 

Mà x ≠ 0 và x là số nhỏ nhất nên:

\(x\in BCNN\left(14,21\right)\)

Ta có: 

\(14=2\cdot7\)

\(21=3\cdot7\)

\(\Rightarrow x=BCNN\left(14,21\right)=7\cdot2\cdot3=42\)

b) \(200-\left(2x+6\right)=4^3\)

\(\Rightarrow2x+6=200-4^3\)

\(\Rightarrow2x+6=200-64\)

\(\Rightarrow2x+6=136\)

\(\Rightarrow2x=136-6\)

\(\Rightarrow2x=130\)

\(\Rightarrow x=130:2\)

\(\Rightarrow x=65\)

2³.5 + 3¹⁹ : 3¹⁷ - 2022⁰

= 8.5 + 3² - 1

= 40 + 9 - 1

= 48

2^3 * 5+3^19:3^17-2022^0

= 8*5+3^19:3^17-1

=8*5+3^2-1

=8*5+9-1

=40+9-1

=48

a) 2; 3; 4

b) 1; 2; 3

Số số hạng của A:

(100 - 2) : 2 + 1 = 50 (số)

A = 2 - 4 + 6 - 8 + ... + 98 - 100

= (2 - 4) + (6 - 8) + ... + (98 - 100)

= -2 . 50 : 2

= -50

a) x - 1/2 = 3/5

x = 3/5 + 1/2

x = 11/10

b) x - 1/2 = -2/3

x = -2/3 + 1/2

x = -1/6

c) 2/5 - x = 0,25

x = 2/5 - 0,25

x = 2/5 - 1/4

x = 3/20

\(d,-\dfrac{3}{26}.\left(-\dfrac{15}{19}\right)+\dfrac{2}{19}.\left(-\dfrac{3}{26}\right)\\=-\dfrac{3}{26}.\left(-\dfrac{15}{19}+\dfrac{2}{19}\right)\\ =-\dfrac{13}{19}.\left(-\dfrac{3}{26}\right)\\ =\dfrac{3}{38}. \)

d) \(\dfrac{-3}{26}\times\left(\dfrac{-15}{19}\right)+\dfrac{2}{19}\times\dfrac{-3}{26}\)

\(=\dfrac{-3}{26}\times\left[\left(\dfrac{-15}{19}\right)+\dfrac{2}{19}\right]\)

\(=\dfrac{-3}{26}\times\dfrac{-13}{19}\)

\(=\dfrac{3}{38}\)

Câu 9

a) 2/15 + (-3/5)

= 2/15 - 3/5

= 2/15 - 9/15

= -7/15

b) -5/7 + 3/7 . (-2/9)

= -5/7 - 2/21

= -15/21 - 2/21

= -17/21

c) 5/16 - (7/15 - 3/16) + 17/30

= 5/16 - 7/15 + 3/16 + 17/30

= (5/16 + 3/16) + (17/30 - 14/30)

= 1/2 + 1/10

= 5/10 + 1/10

= 6/10

= 3/5

\(a,\dfrac{2}{15}+\left(-\dfrac{3}{5}\right)\\ =\dfrac{2}{15}-\dfrac{3}{5}\\ =\dfrac{2}{15}-\dfrac{9}{15}\\ =-\dfrac{7}{15}\\ b,-\dfrac{5}{7}+\dfrac{3}{7}\times\left(-\dfrac{2}{9}\right)\\ =-\dfrac{5}{7}-\dfrac{2}{21}\\ =-\dfrac{15}{21}-\dfrac{2}{21}\\ =-\dfrac{17}{21}\\ c,\dfrac{5}{16}-\left(\dfrac{7}{15}-\dfrac{3}{16}\right)+\dfrac{17}{30}\\ =\dfrac{5}{16}-\dfrac{7}{15}+\dfrac{3}{16}+\dfrac{17}{30}\\ =\left(\dfrac{5}{16}+\dfrac{3}{16}\right)-\left(\dfrac{17}{15}+\dfrac{17}{30}\right)\\ =\dfrac{1}{2}-\dfrac{17}{10}\\ =\dfrac{5}{10}-\dfrac{17}{10}\\ =-\dfrac{6}{5}.\)