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2 tháng 12 2018

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

12 tháng 8 2017

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 ....

6 tháng 12 2016

may cai bai day ma cung khong biet oc cho

6 tháng 12 2016

a) 89-(73-x)=20

=>73-x=89-20

=>73-x=69

=>x=73-69

=>x=4

9 tháng 8 2018

bài 1) thực hiện phép tính

a) \(4^5-81:3^2=1024-9=1015\)

b) \(3^2.22-3^2.12=3^2.2\left(11-6\right)=18.5=90\)

c) \(2^3.15-\left[115-\left(12-5\right)\right]=120-\left(115-12+5\right)=120-115+12-5=12\)

d) \(3.3^2-19^{21}:19^{20}+2010^0=27-19+1=9\)

e)\(7^{25}:\left(7^{21}.46+7^{21}.3\right)=7^{25}:\left(7^{21}.49\right)=\frac{7^{21}.7^4}{7^{21}.49}=\frac{2401}{49}=49\)

bài 2)Tim x

a) 716 - (x - 143) = 695

<=> x - 143 = 716 - 695

<=> x - 143 = 21

<=> x = 21 + 143

<=> x = 164

vậy x = 164

20 tháng 9 2018

a) 7.x - x = 521 : 519 + 3.22 - 70

6x = 25 + 12 - 1

6x = 36

x = 6

b) 7x - 2x = 617 : 615 + 44 : 11

5x = 36 + 4

5x = 40

x = 8

20 tháng 9 2018

c) 5x + x = 39 - 311 : 39

6x = 39 - 9

6x = 30

x = 5

d) [(6x - 39) : 7]. 4 = 12

(6x - 39) : 7 = 12 : 4

(6x - 39) : 7 = 3

6x - 39 = 3 . 7

6x - 39 = 21

6x = 21 + 39

6x = 60

x = 10

x = 

17 tháng 7 2016

125 : 5^2 . (x-3) = 3

125 : 25 .(x-3) = 3

5 (x-3) =3

x-3 = 3 : 5

Đề bài sai hay sao ý?

2x -5 = 3

2x = 3+5 =8

x =4

 (19 .x+2.5^2 ): 14 = (13-8)^2 - 4^2

19x + 50) : 14 = 25 - 16

(19x+50) : 14 = 9

19x+50 = 3*14 = 126

 19x = 126-50 = 76

x = 76 / 19 = 4

17 tháng 7 2016

\(a\)\(125:5^2.\left(x-3\right)=3\)

\(5^3:5^2.\left(x-3\right)=3\)

\(5.\left(x-3\right)=3\)

\(5x-15=3\)

\(5x=3+15\)

\(5x=18\)

\(x=\frac{18}{5}\)\(.\)Vậy \(x=\frac{18}{5}\)

\(b\)\(\left(2x-5\right)^3=27\)

\(\left(2x-5\right)^3=3^3\)

\(\Rightarrow2x-5=3\)

\(\Rightarrow2x=8\)

\(\Rightarrow x=4\)\(.\)Vậy \(x=4\)

\(c\))\(\left(19.x+2.5^2\right):14=\left(13-8\right)^2-4^2\)

\(\left(19.x+2.25\right):14=5^2-16\)

\(\left(19.x+2.25\right):14=25-16\)

\(\left(19.x+50\right):14=9\)

\(19.x+50=126\)

\(19.x=126-50\)

\(19.x=76\)

\(x=76:19\)

\(x=4\)\(.\)Vậy \(x=4\)

21 tháng 9 2018

( 5 . 2 mũ 2 - 20 ) : 5

22 tháng 10 2019

1. \(6x^3-8=40\\ 6x^3=48\\ x^3=8\\ \Rightarrow x=2\)Vậy x = 2

2. \(4x^5+15=47\\ 4x^5=32\\ x^5=8\\ \Rightarrow x\in\varnothing\left(\text{vì }x\in N\right)\)Vậy x ∈ ∅

3. \(2x^3-4=12\\ 2x^3=16\\ x^3=8\\ \Rightarrow x=2\)Vậy x = 2

4. \(5x^3-5=0\\ 5x^3=5\\ x^3=1\\ \Rightarrow x=1\)Vậy x = 1

5. \(\left(x-5\right)^{2016}=\left(x-5\right)^{2018}\\ \Rightarrow\left[{}\begin{matrix}x-5=0\\x-5=1\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=5\\x=6\end{matrix}\right.\)Vậy \(x\in\left\{5;6\right\}\)

6. \(\left(3x-2\right)^{20}=\left(3x-1\right)^{20}\\ \Rightarrow3x-2=3x-1\\ 3x-3x=2-1\\ 0=1\left(\text{vô lí}\right)\)Vậy x ∈ ∅

7. \(\left(3x-1\right)^{10}=\left(3x-1\right)^{20}\\ \left(3x-1\right)^{10}=\left[\left(3x-1\right)^2\right]^{10}\\ \Rightarrow\left(3x-1\right)^2=3x-1\\ \left(3x-1\right)^2-\left(3x-1\right)=0\\ \left(3x-1\right)\left[\left(3x-1\right)-1\right]=0\\ \left(3x-1\right)\left(3x-2\right)=0\\ \Rightarrow\left[{}\begin{matrix}3x-1=0\\3x-2=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}3x=1\\3x=2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\frac{1}{3}\left(\text{loại vì }x\in N\right)\\x=\frac{2}{3}\left(\text{loại vì }x\in N\right)\end{matrix}\right.\)Vậy x ∈ ∅

8. \(\left(2x-1\right)^{50}=2x-1\\ \left(2x-1\right)^{50}-\left(2x-1\right)=0\\ \left(2x-1\right)\left[\left(2x-1\right)^{49}-1\right]=0\\ \Rightarrow\left[{}\begin{matrix}2x-1=0\\\left(2x-1\right)^{49}=1\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x=1\\2x-1=1\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=\frac{1}{2}\left(\text{loại vì }x\in N\right)\\x=1\left(t/m\right)\end{matrix}\right.\)Vậy x = 1

9. \(\left(\frac{x}{3}-5\right)^{2000}=\left(\frac{x}{3}-5\right)^{2008}\\ \left(\frac{x}{3}-5\right)^{2008}-\left(\frac{x}{3}-5\right)^{2000}=0\\ \left(\frac{x}{3}-5\right)^{2000}\left[\left(\frac{x}{3}-5\right)^8-1\right]=0\\ \Rightarrow\left[{}\begin{matrix}\left(\frac{x}{3}-5\right)^{2000}=0\\\left(\frac{x}{3}-5\right)^8=1\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}\frac{x}{3}-5=0\\\frac{x}{3}-5=1\\\frac{x}{3}-5=-1\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}\frac{x}{3}=5\\\frac{x}{3}=6\\\frac{x}{3}=4\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=5\cdot3=15\\x=6\cdot3=18\\x=4\cdot3=12\end{matrix}\right.\)Vậy \(x\in\left\{15;18;12\right\}\)

22 tháng 10 2019

\(1.6x^3-8=40\\ \Leftrightarrow6x^3=48\\ \Leftrightarrow x^3=8\Leftrightarrow x^3=2^3=\left(-2\right)^3\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-2\end{matrix}\right.\)

Vậy \(x\in\left\{2;-2\right\}\)

\(2.4x^3+15=47\) (T nghĩ đề là mũ 3)

\(\Leftrightarrow4x^3=32\Leftrightarrow x^3=8=2^3=\left(-2\right)^3\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-2\end{matrix}\right.\)

Vậy \(x\in\left\{2;-2\right\}\)

Câu 3, 4 tương tự nhé.