a, 1230 : 3(x – 20) = 10

3(x – 20) = 123

x – 20 = 41

x = 61

b, 250 – 10.(24 – 3x):15 = 244

10.(24 – 3x):15 = 6

10.(24 – 3x) = 90

24 – 3x = 9

3x = 15

x = 5

c,  4 x 3  + 15 = 47

4 x 3 = 32

x 3 = 8 = 2 3

x = 2

d,  65 - 4 x + 2 = 2014 0

65 - 4 x + 2 = 1

4 x + 2 = 64 = 4 3

x + 2 = 3

x = 1

e,  4 . 2 x - 3 = 125

4 . 2 x = 128

2 x = 32 = 2 5

x = 5

1: =>\(5^{2x-3}=5^2\cdot3+5^2\cdot2=5^2\cdot5=5^3\)

=>2x-3=3

=>2x=6

=>x=3

2: \(41-2^{x+1}=9\)

=>\(2^{x+1}=32\)

=>x+1=5

=>x=4

3: =>\(4^{x+2}=65-1=64\)

=>x+2=3

=>x=1

\(5^{2x-3}-2.5^2=5^2.3\\ 5^{2x-3}=5^2.3+5^2.2\\ 5^{2x-3}=5^2.\left(3+2\right)\\ 5^{2x-3}=5^2.5\\ 5^{2x-3}=5^3\\ \Rightarrow2x-3=3\\ 2x=3+3\\ 2x=6\\ x=\dfrac{6}{2}\\ Vậy:x=3\)

\(41-2^{x+1}=9\\ 2^{x+1}=41-9\\ 2^{x+1}=32=2^5\\ \Rightarrow x+1=5\\ \Leftrightarrow x=5-1=4\\ ---\\ 65-4^{x+2}=2014^0\\ 65-4^{x+2}=1\\ 4^{x+2}=65-1\\ 4^{x+2}=64=4^3\\ \Rightarrow x+2=3\\ Vậy:x=1\)

a) 52x - 3 - 2 . 52 = 52 . 3

x - 3/52 - 2 = 3

x = 3 + 2 + 3/52

x = 263/52

b) 740 / (x + 10) = 102 - 2 . 13

740 / (x + 10) = 76

x + 10 = 740 / 76

x + 10 = 185/19

x = 185/19 - 10

x = -5/19

c) 65 - 4x + 2 = 20140

65 - 4x = 20140 - 2

65 - 4x = 20138

4x = 65 - 20138

4x = -20073

x = -20073/4

d) 120 + 2 . (3x - 17) = 214

60 + 3 . x - 17 = 107

20 + x - 17/3 = 107/3

20 + x = 107/3 + 17/3

20 + x = 124/3

x = 124/3 - 20

x = 64/3

e) 41 - 2x + 1 = 9

42 - 2x = 9

21 - x = 9/2

x = 21 - 9/2

x = 33/2

a: =>4x^2-24x+36-4x^2+4x-1<10

=>-20x<10-35=-25

=>x>=5/4

b: =>x(x^2-25)-x^3-8<=3

=>x^3-25x-x^3-8<=3

=>-25x<=11

=>x>=-11/25

a) \(\left(x-3\right)^2+\left(4-x\right)\left(x+4\right)=10\)

\(\Leftrightarrow\left(x^2-2\cdot x\cdot3+3^2\right)+\left(4-x\right)\left(4+x\right)=10\)

\(\Leftrightarrow x^2-6x+9+\left(4^2-x^2\right)-10=0\)

\(\Leftrightarrow x^2-6x-1+16-x^2=0\)

\(\Leftrightarrow-6x+15=0\)

\(\Leftrightarrow6x=15\)

\(\Leftrightarrow x=\dfrac{5}{2}\)

b) \(x^2-2x=0\)

\(\Leftrightarrow x\left(x-2\right)=0\)

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

c) \(\left(x^2-9\right)^2-\left(x-3\right)^2=0\)

\(\Leftrightarrow\left(x^2-3^2\right)^2-\left(x-3\right)^2=0\)

\(\Leftrightarrow\left(x-3\right)^2\left(x+3\right)^2-\left(x-3\right)^2=0\)

\(\Leftrightarrow\left(x-3\right)^2\left[\left(x+3\right)^2-1\right]=0\)

\(\Leftrightarrow\left[{}\begin{matrix}\left(x-3\right)^2=0\\\left(x+3\right)^2-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x-3=0\\\left(x+3\right)^2=1\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x+3=1\\x+3=-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-2\\x=-4\end{matrix}\right.\)

C

\(x^2+3x-4x-12=x^2-x-12\)

Chọn C

ai nhanh nhất mình k cho

Bài 1:

\(A=\frac{1}{\left(1+2\right)}+\frac{1}{\left(1+2+3\right)}+\frac{1}{\left(1+2+3+4\right)}\)\(+\frac{1}{\left(1+2+3+4+5\right)}+...+\)\(\frac{1}{\left(1+2+3+...+10\right)}\)

\(A=\frac{1}{3}+\frac{1}{6}+....+\frac{1}{55}\)

\(A=2\left(\frac{1}{6}+\frac{1}{12}+....+\frac{1}{110}\right)\)

\(A=2\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{10.11}\right)\)

\(A=2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{10}-\frac{1}{11}\right)\)

\(A=2.\left(\frac{1}{2}-\frac{1}{11}\right)\)

\(A=\frac{9}{11}\)

Bài 2 :

2)  Tử số = 11 x 13 x 15 + 3 x 3 x 3 x 11 x 13 x 15 + 5 x 5 x 5 x 11 x 13 x 15 + 9 x 9 x 9 x 11 x 13 x 15

= (1 + 3 x 3 x 3 + 5 x 5 x 5 + 9 x 9 x9) x 11 x 13 x 15 = (1+27+125+ 729) x 11 x 13 x 15

Mẫu số =  11 x 13 x 17 + 3 x 3 x 3 x 13 x 15 x 19  + 5 x 5 x 5 x 13 x 15 x 17 + 9 x 9 x 9 x 13 x 15 x 17 lớn hơn 11 x 13 x 15 + 3 x 3 x 3 x 13 x 15 x 17 + 5 x 5 x 5 x 13 x 15 x 17 + 9 x 9 x 9 x 13 x 15 x 17  

=  (1 + 3 x 3 x 3 + 5 x 5 x 5 + 9 x 9 x9) 13 x 15 x  17 = (1+27+125+729) x 13 x 15 x 17 

\(\Rightarrow A< \frac{\left(1+27+125+729\right)\times11\times13\times15}{\left(1+27+125+729\right)\times13\times15\times17}\)

\(=\frac{11}{17}\)

\(=\frac{1111}{1717}=B\)

Vậy \(A=B\)

mình đâu biết

a: =>3x=10+14=24

=>x=8

b: =>25-30-x=-19

=>-5-x=-19

=>x+5=19

=>x=14

c: =>15-x=12+14=26

=>x=-11

d: =>4x+11-x-34=67

=>3x-23=67

=>3x=90

=>x=30

e: =>-x-14=289-36-289=-36

=>x+14=36

=>x=22

a) 3x=24
     x=8
b) 25-30-x=-19
    25-30+19=x
     14=x
c) 15-x=26
         x=-11
d) 4x+11-x-34=67
    3x=90
      x=30
e) -14-x= -36
          x=-14 -36
          x= 22