Question

tìm x biết;

a) 121-3.(x-5)=6

b)2x-138=2\(^3\) . 3\(^2\) 

c) (x-3)⋮7 và 10<x<50

d) 27⋮(x+1)

Answer 1

Lời giải:

a. $121-3(x-5)=6$

$3(x-5)=121-6=115$

$x-5=115:3=\frac{115}{3}$

$x=\frac{115}{3}+5=\frac{130}{3}$

b.

$2x-138=2^3.3^2=72$

$2x=72+138=210$

$x=210:2=105$

c.

$x-3\vdots 7$

$\Rightarrow x-3\in\left\{0;7;14;21;28;35;42;49; 56;...\right\}$

Mà $10< x< 50$ nên $x\in\left\{14;21;28;35;42;49\right\}$

d.

$27\vdots x+1$

$\Rightarrow x+1\in\left\{\pm 1; \pm 3; \pm 9; \pm 27\right\}$

$\Rightarrow x\in\left\{0; -2; -4; 2; 8; -10; 26; -28\right\}$

Answer 2

a ) 121-3.(x - 5 ) = 6

3.(x-5) = 121 -6

3. (x-5)=115

x-5  = 115:3

x-5=35

x=35+5

x = 40

b) 2x - 138 = 2'3. 3'2

2x -138=8.9

2x-138=72

2x=72+138

2x=210

x=210:2

x=105

c) theo bài ra : x-3 ∈ B(7)

ta có B(7)=(0,7,14,21,28,35,49,56,...)

=) x-3 ∈ ( 0,7,14,21,28,35,49,56,...)

=) x ∈( 3 , 10,17,24,31,38,42,58,..)

mà 10 <x<50 nên x ∈ ( 17 , 24 ,31,38,42 )

vậy x ∈(17,24,31,38,42)

Answer 3

Lời giải:

a. $121-3(x-5)=6$

$3(x-5)=121-6=115$

x-5=115:3=\frac{115}{3}x−5=115:3=3115​

x=\frac{115}{3}+5=\frac{130}{3}x=3115​+5=3130​

b.

2x-138=2^3.3^2=722x−138=23.32=72

$2x=72+138=210$

$x=210:2=105$

c.

$x-3⋮7$

$\Rightarrow x-3\in \left\{0;7;14;21;28;35;42;49;56;...\right\}$

Mà $10<x<50$ nên $x\in \left\{14;21;28;35;42;49\right\}$

d.

$27⋮x+1$

$\Rightarrow x+1\in \left\{\pm 1;\pm 3;\pm 9;\pm 27\right\}$

$\Rightarrow x\in \left\{0;-2;-4;2;8;-10;26;-28\right\}$

Answer 4

d) theo bài ra : x+1 ∈ Ư(27)

ta có Ư(27)=(1,3,9,27)

x+1 ∈ (1,3,9,27)

x ∈ (0,2,8,26 )

vậy x ∈ (0,2,8,26)