1. tìm x 

kết quả x là : 2010

2. tìm x 

a) x = 13

b) x = 6

đúng ko

câu 3 số lớn quá

1.

1(1+2+3+4+....+x)=2021055

   1+2+3+4+....+x=2021055:1=2021055

x+(x+1)/1=2021055

=>x(x+1)=1*2021055=2021055=2011*2010  =>x=2010

3.Tìm số dư123456789987654321 : 2015

123456789:2015=61268,R= 1769

176998765:2015=87840,R= 1165

11654321:2015=5783,R= 1576

Vậy số dư của phép chia 123456789987654321:2015 là 1576

c: -62+x=-14+46

=>\(x-62=46-14=32\)

=>\(x=32+62=94\)

d: \(25+\left(x-5\right)=-123-\left(15-123\right)\)

=>\(x-5+25=-123-15+123\)

=>\(x+20=-15\)

=>\(x=-15-20=-35\)

`c) -62 + x = -14 + 46`

`-62 + x = 32`

`x = 32 - (-62)`

`x = 94`

Vậy `x = 94`

`d) 25 + ( x - 5 ) = -123 - ( 15 - 123 )`

`25 + ( x - 5 ) = -123 - 15 + 123`

`25 + ( x - 5 ) = - 15`

`x - 5 = -15 - 25`

`x - 5 = -40`

`x = -40 + 5`

`x = -35`

Vậy `x = -35`

5,10,15,30

=> 143 - 3 chia hết cho x

140 chia hết cho x

=> 123 - 23 chia hết cho x 

100 chia hết cho x

=> x thuộc ƯC(140 ; 100)

UCLN(140 ; 100) = 20 

Vậy x thuộc {1;2;4;5;10;20} 

`123-5(x+4)=38`

`5x-20=123-38`

`5x-20=85`

`5x=85+20`

`5x=105`

`x=105:5`

`x=21`

123-5.(x+4)=38

         5x-20=123-38

         5x-20=85

               5x=85+20

               5x=105

                 x=105:5

                x=21

x=(50343-123):405
x=50220:405
x=124

x=50343-123) :405

x=50220 :405

x=124

x= 124 nha

HT

a: =>x*21=3885:37=105

=>x=105:21=5

b: 50343:x=405 dư 123

=>x=(50343-123)/405=124

a, 3885 : (X x 21) = 37
=> 21X = 3885/37
=> 21X = 105
=> X = 5
b, 50343 : X = 405 (dư 123)
=> X = 50343 : 405 + 123
=> X = 33386/135

a) \(3885:\left(x\times21\right)=37\)

\(x\times21=3885:37\)

\(x\times21=105\)

\(x=105:21=5\)

b) \(50343:x=405\)(dư 123)

=> \(405\times x+123=50343\)

\(405\times x=50343-123\)

\(405\times x=50220\)

\(x=50220:405=124\)

\(\Leftrightarrow\dfrac{5}{4}\left(\dfrac{4}{3\cdot7}+\dfrac{4}{7\cdot11}+...+\dfrac{4}{x\left(x+4\right)}\right)=\dfrac{50}{123}\)

=>(1/3-1/7+1/7-1/11+...+1/x-1/x+4)=50/123:5/4=50/123*4/5=40/123

=>1/3-1/x+4=40/123

=>1/x+4=1/123

=>x+4=123

=>x=119

a) x-12=-15
x=-15+12
x=-3
b) 123-5(x+4)=38
5(x+4)=123-38
5(x+4)=85
x+4=85:5=17
x=17-4
x=13

\(a.x-12=-15\)                    \(b.123-5.\left(x+4\right)=38\)

\(x=\left(-15\right)+12\)                        \(5.\left(x+4\right)=123-38\)

\(x=-3\)                                      \(5.\left(x+4\right)=85\)           

                                                   \(x+4=85:5=17\)

                                                    \(x=17-4=13\)

a) x-12=-15
x=-15+12
x=-3
b) 123-5(x+4)=38
5(x+4)=123-38
5(x+4)=85
x+4=85:5=17
x=17-4
x=13