30,31

36+1

20

88

Bài 23: Tìm x:

a) 29 < 30 < 32

b) 36 < 37 + 1 < 39

c) 30 + 30 < 64

d) 46 < 88 - 42 < 48

a, 30

b,37

c, 30

d, 88

a) Ta có: \(\left(2x-1\right)\left(x^2-x+1\right)=2x^3-3x^2+2\)

\(\Leftrightarrow2x^3-2x^2+2x-x^2+x-1-2x^3+3x^2-2=0\)

\(\Leftrightarrow3x=3\)

hay x=1

Vậy: S={1}

b) Ta có: \(\left(x+1\right)\left(x^2+2x+4\right)-x^3-3x^2+16=0\)

\(\Leftrightarrow x^3+2x^2+4x+x^2+2x+4-x^3-3x^2+16=0\)

\(\Leftrightarrow6x=-20\)

hay \(x=-\dfrac{10}{3}\)

c) Ta có: \(\left(x+1\right)\cdot\left(x+2\right)\left(x+5\right)-x^3-8x^2=27\)

\(\Leftrightarrow\left(x^2+3x+2\right)\left(x+5\right)-x^3-8x^2-27=0\)

\(\Leftrightarrow x^3+5x^2+3x^2+15x+2x+10-x^3-8x^2-27=0\)

\(\Leftrightarrow17x=17\)

hay x=1

a: 5x=9,5

nên x=1,9

b: 42x=15,12

nên x=15,12:42=0,36

a, \(x=\dfrac{9,5}{5}=\dfrac{19}{10}\)

b, \(x=\dfrac{15,12}{42}=\dfrac{9}{25}\)

a.\(x\times5=9,5\)

\(\Rightarrow x=9,5:5=1,9\)

b.\(42\times x=15,12\)

\(\Rightarrow x=15,12:42=0,36\)

\(a,ƯC\left(40,24\right)=Ư\left(8\right)=\left\{...\right\}\\ b,ƯC\left(12,52\right)=Ư\left(4\right)=\left\{...\right\}\\ c,ƯC\left(36,990\right)=Ư\left(18\right)=\left\{...\right\}\\ d,ƯC\left(54,36\right)=Ư\left(9\right)=\left\{...\right\}\\ e,ƯC\left(10,20,70\right)=Ư\left(10\right)=\left\{...\right\}\\ f,ƯC\left(25,55,75\right)=Ư\left(5\right)=\left\{...\right\}\\ g,ƯC\left(80,144\right)=Ư\left(16\right)=\left\{...\right\}\\ h,ƯC\left(63,2970\right)=Ư\left(9\right)=\left\{...\right\}\\ i,ƯC\left(65,125\right)=Ư\left(5\right)=\left\{...\right\}\\ j,ƯC\left(9,18,72\right)=Ư\left(9\right)=\left\{...\right\}\\ k,ƯC\left(24,36,60\right)=Ư\left(12\right)=\left\{...\right\}\\ l,ƯC\left(16,42,86\right)=Ư\left(2\right)=\left\{..\right\}\)

a:UC(40;24)=Ư(8)

b: UC(12;52)=Ư(4)

Bài 3a) 576 + 678 + 780 - 475 - 577 - 679

= ( 578 - 475 ) + ( 678 - 577 ) + ( 780 - 679 )

= 103 + 101 + 101

= 305

b) ( 126 + 32 ) x ( 18 - 16 - 2 ) 

= 158 x 0 

= 0 

c) 36 x 17 + 12 x 34 + 6 x 30 

= 6 x 6 x 17 + 6 x 2 x 34 + 6 x 30

= 6 x 102 + 6 x 68 + 6 x 30

= 6 x ( 102 + 68 + 30 )

= 6 x 200

= 1200

Bài 4:a. x × 6 = 3048 : 2

x × 6 = 1524

x = 1524 : 6

x = 254

b. 56 : x = 1326 – 1318

56 : x = 8

x = 56 : 8

x = 7

Bài 4: 

a) Ta có: \(x\cdot6=3048:2\)
nên 6x=1524

hay x=254

b) Ta có: 56:x=1326-1318

nên 56:x=8

hay x=7

\(a,x.4,25=7\\ \Rightarrow x=7:4,25\\ \Rightarrow x=\dfrac{28}{17}\\ b,116:x=14,5\\ \Rightarrow x=116:14,5\\ \Rightarrow x=8\\ c,15.x=8\\ \Rightarrow x=\dfrac{8}{15}\\ c,729:x=36\\ \Rightarrow x=729:36\\ \Rightarrow x=20,25\)

Tìm x:

a) x . 4,25 = 17 

x = 17 : 4,25

x = 4

b) 116 : x = 14,5

x = 116 : 14,5

x = 8

c) 15 . x = 8 

x = 8 : 15

x = 0.53333333333

d) 729 : x = 36

x = 729 : 36

x = 20.25

a ) − 1 2 ≤ x < 2 3 = > x = 0. b ) − 1 < x ≤ 1 = > x ∈ {0;1}