a, 245 - 5 . ( 16 + x ) = 140

              5 . ( 16 + x ) = 245 - 140

              5  . ( 16 + x ) = 145

                     16 + x     = 145 : 5

                     16 + x     = 29 

                             x      = 29 - 16

                             x      = 13 .

b, ( x - 1945 ) . 5  = 50

     x - 1945           = 50 : 5

     x - 1945           = 10

            x                = 10 + 1945

           x                 = 1955 .

c, 30 . ( 60 - x ) = 30

            60 - x     = 30 : 30

           60 - x      = 1

                  x       = 60 - 1

                  x       = 59 .

d, [ ( 250 - 25 ) : 15 ] : x = ( 450 - 60 ) : 130

    [ 225 : 15 ]             : x  = 390 : 130

       15                        : x  =  3

                                     x  = 15 : 3

                                     x  = 5 .

e, x : [ ( 1800 + 600 ) ] = 560 : ( 315 - 35 )

    x : 2400                     = 560 : 280

    x : 2400                     = 2

    x                                 = 2 . 2400

    x                                 = 4800 .

f, x . ( x + 1 ) = 2 + 4 + 6 + 8 + 10 + ... + 2500

2 + 4 + 6 + 8 + 10 + ... + 2500

 Số số hạng của dãy số trên là :

       ( 2500 - 2 ) : 2 + 1 = 1250 ( số hạng )

=> 2 + 4 + 6 + 8 + 10 + 2500

= ( 2 + 2500 ) . 1250 : 2

= 2502 . 1250 : 2

= 3127500 : 2

= 1563750 .

Ta có :

x . ( x + 1 ) = 1563750

Mà : 1563750 = 1250 . 1251

=> x = 1250 .

a) 450 – ( 25 – 10) = 450 – 15

                   = 435

450 – 25 – 10 = 425 – 10

                   = 415

b) 180 : 6 : 2 = 30 : 6

                   = 15

180 : ( 6 : 2 ) = 180 : 3

                   = 60

c) 410 – (50 +30) = 410 -80

                   = 330

410 - 50 + 30 = 360 + 30

                   = 390

d) 16 x (6 : 3) = 16 x 2

                   = 32

16 x 6 : 3 = 96 : 3

                   = 32

Phải cho đề bài chứ. 

(X -10/1994 -1) + (X-8/1996 - 1) + (X-6/1998 - 1)+ (X-4/2000 - 1) + (X-2/2002 - 1) = (X-2002/2 - 1) + (X-2000/4 - 1) + (X-1998/6 - 1) + (X-1996/8 - 1) + (X-1994/10 - 1) 

=> x-2004/1994 + x-2004/1996 + x-2004/1998 + x-2004/2000 + x-2004/2002 = x-2004/2 + x-2004/4 + x-2004/6 + x-2004/8 + x-2004/1994 

=> x-2004/1994 + x-2004/1996 + x-2004/1998 + x-2004/2000 + x-2004/2002 - x-2004/2 -  x-2004/4 - x-2004/6 - x-2004/8 -  x-2004/1994 = 0 

=>  (x - 2004)(1/994 + 1/1996 + 1/1998 + 1/2000 + 1/2002 + 1/2 +  1/4 + 1/6 + 1/8) = 0 

Mà  (1/994 + 1/1996 + 1/1998 + 1/2000 + 1/2002 + 1/2 +  1/4 + 1/6 + 1/8) \(\ne\)0 

=> x - 2004 = 0 

=> x = 2004 

Vậy x = 2004 

Sửa (x  - 2004)  (1/1994 + 1/1996 + 1/1998/+ 1/2000 + 1/2002 + 1/2 + 1/4 +  1/6+ 1/8 + 1/10) 

 = (x - 2004) (1/1994 + 1/1996 + 1/1998/+ 1/2000 + 1/2002 - 1/2 -1/4 -  1/6 -  1/8 - 1/10) 

 :)))

`(3xx4xx7)/(5xx3xx4)=7/5`

`(2xx5xx6xx8)/(6xx2xx8xx9)=5/9`

`(4xx5xx6)/(3xx10xx8)= (4xx5xx6)/(3xx5xx2xx4xx2)= 6/(3xx2xx2)= 6/(6xx2)=1/2`

\(a,\dfrac{3\times4\times7}{5\times3\times4}=\dfrac{7}{5}\)

\(b,\dfrac{2\times5\times6\times8}{6\times2\times8\times9}=\dfrac{5}{9}\)

\(c,\dfrac{4\times5\times6}{3\times10\times8}=\dfrac{2}{4}=\dfrac{1}{2}\)

1/ 10(X-7)-8(X+5)=6(-5)+24
10x - 70 - 8x - 40 = -30 +24
2x - 110 = -6
2x = 104
x=52

2/ 8(X-|-7|)-6(X-2)=|-8|.6-50
8(x - 7) - 6(x-2) = 8.6 - 50
8x - 56 - 6x +12 =48 -50
2x - 44 = -2
2x = 42
x=21

3/ 2(4X-8)-7(3+X)=|-4|(3-2)
8x-16 - 21 - 7x = 4.1
x-37=4
x=41

4/ 12(X-4)=6(x-2)-16(X+3)=7|-4|
12x - 48 = 6x - 12 - 16x -48 =7.4
12x - 48 = 28
12x=76
x=19/3

5/ 4(X-5)-7(5-X)+10(5-X)=-3
4x - 20 -35 +7x + 50 -10x = -3
x - 5 = -3
x = -2
Chúc bạn học tốt!

\(x^2=1\Rightarrow\left[{}\begin{matrix}x=-1\\x=1\end{matrix}\right.\)

\(x^2=3\Rightarrow\left[{}\begin{matrix}x=-\sqrt{3}\\x=\sqrt{3}\end{matrix}\right.\)

\(x^2=5\Rightarrow\left[{}\begin{matrix}x=-\sqrt{5}\\x=\sqrt{5}\end{matrix}\right.\Rightarrow x=-\sqrt{5}\left(vì.x< 0\right)\)

\(x^2=7\Rightarrow\left[{}\begin{matrix}x=-\sqrt{7}\\x=\sqrt{7}\end{matrix}\right.\Rightarrow x=-\sqrt{7}\left(vì.x< 0\right)\)

\(x^2=9\Rightarrow\left[{}\begin{matrix}x=-3\\x=3\end{matrix}\right.\)

\(\left(x-2\right)^2=2\Rightarrow\left[{}\begin{matrix}x-2=-\sqrt{2}\\x-2=\sqrt{2}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=2-\sqrt{2}\\x=2+\sqrt{2}\end{matrix}\right.\)

\(\left(x-4\right)^2=4\Rightarrow\left[{}\begin{matrix}x-2=-2\\x-2=2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=4\end{matrix}\right.\)

\(\left(x-6\right)^2=6\Rightarrow\left[{}\begin{matrix}x-6=-\sqrt{6}\\x-6=\sqrt{6}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=6-\sqrt{6}\\x=6+\sqrt{6}\end{matrix}\right.\)

\(\left(x-8\right)^2=8\Rightarrow\left[{}\begin{matrix}x-8=-2\sqrt{2}\\x-8=2\sqrt{2}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=8-2\sqrt{2}\\x=2+2\sqrt{2}\end{matrix}\right.\)

\(\left(x-10\right)^2=10\Rightarrow\left[{}\begin{matrix}x-10=-\sqrt{10}\\x-10=\sqrt{10}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=10-\sqrt{10}\\x=10+\sqrt{10}\end{matrix}\right.\)

\(\left(x-\sqrt{3}\right)^2=3\Rightarrow\left[{}\begin{matrix}x-\sqrt{3}=-\sqrt{3}\\x-\sqrt{3}=\sqrt{3}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=2\sqrt{3}\end{matrix}\right.\)

\(\left(x-\sqrt{5}\right)^2=5\Rightarrow\left[{}\begin{matrix}x-\sqrt{5}=-\sqrt{5}\\x-\sqrt{5}=\sqrt{5}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=2\sqrt{5}\end{matrix}\right.\)

 11 x 10 - 10 x 9 + 9 x 8 - 8 x 7 + 7 x 6 - 6 x 5 + 5 x 4 - 4 x 3 + 3 x 2 - 2 x 1 = 60