( 5 . 2 mũ 2 - 20 ) : 5

a) x(x+1)=2+4+6+8+...+2500

x(x+1)=(2500+2).1250:2

x(x+1)=1563750

Ta thấy: x và x+1 là 2 số liên tiếp

Mà x(x+1)=1563750=>x=1250;x+1=1251

Vậy x=1250

b) x-3=12:{390:[500-(5^3+7^2.5)]}

x-3=12:[390:(500-254.64)]

x-3=12:(390:245.35)

x-3=12:1.58

x-3=7.54

=>x=10.5

Vậy x=10.5

c) x+3^3.12=3^3.19

=>x=2.46

Vậy x=2.46

a, \(390-\left(x-7\right)=13^2:12\)

\(390-\left(x-7\right)=\) \(\dfrac{169}{12}\)

\(x-7=390-\dfrac{169}{12}\)

\(x-7=\dfrac{4511}{12}\)

\(x=\dfrac{4511}{12}+7\)

\(x=\dfrac{4595}{12}\)

Vậy ...

b, \(\left(x-35.2^2\right):7=3^3-24\)

\(\left(x-35.4\right):7=27-24\)

\(\left(x-140\right):7=3\)

\(\Leftrightarrow\left(x-140\right)=3.7\)

\(\Leftrightarrow x-140=21\)

\(\Leftrightarrow x=161\)

Vậy .....

c) \(x-6:2-\left(4^2.3-24\right):2:6=3\)

\(x-3-\left(16.3-24\right):2:6=3\)

\(x-3-\left(48-24\right):2:6=3\)

\(x-3-24:2:6=3\)

\(x-3-2=3\)

\(x=3+2+3\)

\(x=8\)

Vậy ......

d) \(4x-5=5+5^2+5^3+.....+5^{99}\)

Đặt :

\(A=5+5^2+.........+5^{99}\)

\(\Leftrightarrow5A=5^2+5^3+..........+5^{100}\)

\(\Leftrightarrow5A-A=\left(5^2+5^3+......+5^{100}\right)-\left(5+5^2+....+5^{99}\right)\)

\(\Leftrightarrow4A=5^{100}-5\)

\(\Leftrightarrow A=\dfrac{5^{100}-5}{4}\)

\(\Leftrightarrow4x+5=\dfrac{5^{100}-5}{4}\)

Đến đây thì sao nữa nhỉ ?

e) \(\left(2x-1\right)^4=625\)

\(\Leftrightarrow\left[{}\begin{matrix}\left(2x-1\right)^4=5\\\left(2x-1\right)^4=-5\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}2x-1=5\\2x-1=-5\end{matrix}\right.\)

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

Vậy ....

   24 : { 390 : [ 500 - ( 125 + 35 . 7 )]} - 3²

= 24 : { 390 : [ 500 - ( 125 +   245 )]} - 9

= 24 : { 390 : [     500     -      370    ]} - 9

= 24 : { 390 :  130} - 9

= 24 :        3           - 9

= 8          -           9 =    -1

k mik nha, thank nhiều nhiều

12 : { 390 - [500 - ( 135 + 35 . 7 ) ] }

= 12 : { 390 - [500 - ( 135 + 245 ) ] } 

= 12 : [ 390 - (500 - 380) ]

= 12 : (390 - 120)

= 12 : 270 

= \(\frac{2}{45}\)

= 12 : {390 : [500 - (125 + 245)]}

= 12 : [390 : (500 - 370)]

= 12 : (390 : 130)

= 12 : 3

= 4

Số cần tìm là:

 4 

  Đ/S: 4

chúc bn học tốt

bằng  4 nha nhé các bạn

Đ/S : 4

k mk nha Huyền

12:{390:[500-(125+35.7)]}

=12:{390:[500-(125+245)]}

=12:{390:[500-370]}

=12:{390:130}

=12:3

=4

            \(12:\left\{390:\left[500-\left(125+35.7\right)\right]\right\}\)                        

      \(=12:\left\{390:\left[500-370\right]\right\}\)

      \(=12:\left[390:130\right]\)

      \(=12:3=4\)

kết quả là 3

12 : ( 390 : ( 500 - ( 125 +35 x 7 )

= 12 : (390 : (500 - (125 + 245) ) )

= 12 : (390 : ( 500 - 370 ) )

= 12 : ( 390 : 130 )

= 12 : 3

= 4 

\(12:\left(390:\left(500-\left(125+35\times7\right)\right)\right)\)

\(=12:\left(390:\left(500-370\right)\right)\)

\(=12:\left(390:130\right)\)

\(=12:3\)

\(=4\)

A = 12 : { 390 : [ 500 - ( 125 + 245 ) ] }

A = 12 : { 390 : [ 500 - 370 ] }

A = 12 : { 390 : 130 }

A = 12 : 3

A = 4