a) \(3^{x+1}=729\)\(\Leftrightarrow3.3^x=729\Rightarrow3^x=243\Rightarrow3^x=3^5\Rightarrow x=5\)

b) \(2^x+2^{x+1}+2^{x+3}=704\Rightarrow2^x+2^x.2+2^x.2^3=704\Rightarrow2^x\left(1+2+8\right)=704\)

\(\Rightarrow2^x.11=704\Rightarrow2^x=64\Rightarrow2^x=2^5\Rightarrow x=5\)

Trả lời

a)2x-15=17

   2x     =17-15

  2x      =2

   x       =2:2

   x       =1

b)3 1/8-1/2x=0,5

    25/8-1/2x=1/2

            1/2x=25/8-1/2

            1/2x=21/8

                 x=21/8.2/1

                 x=21/4

c)8 1/4x+2 1/3=20

   33/4x+7/3     =20

   33/4x            =20-7/3

   33/4x            =53/3

          x            =53/3.4/33

         x             =...

a) 2x - 15 = 17

2x = 17 + 15

2x = 32

x = 32 : 2 

x = 16

Vậy x = 16

b) \(3\frac{1}{3}-\frac{1}{2}x=0,5\)

\(\frac{10}{3}-\frac{1}{2}x=\frac{1}{2}\)

\(\frac{1}{2}x=\frac{10}{3}-\frac{1}{2}\)

\(\frac{1}{2}x=\frac{17}{6}\)

\(x=\frac{17}{6}:\frac{1}{2}\)

\(x=\frac{17}{3}\)

Vậy x = 17/3

c) \(8\frac{1}{4}x+2\frac{1}{3}=20\)

\(\frac{33}{4}x+\frac{7}{3}=20\)

\(\frac{33}{4}x=20-\frac{7}{3}\)

\(\frac{33}{4}x=\frac{53}{3}\)

\(x=\frac{53}{3}:\frac{33}{4}\)

\(x=\frac{212}{99}\)

Vậy x = 212/99

=))

Bài 1: Tìm x , biết :

a) ( x -1).(x-2)=0

<x-1=0

|

<x=0+1=1

-<x-2=0

-<x=0+2=2

Vậy x E {1;2}

b) (x-2).(x^2+1)=0

[<x-2=0

[<x=0+2=2

[>x²+1=0

   x²=0-1

   x²=1.(-1)

c) (x+`1).(x^2-4)=0

Cảm ơn

bài 1:vì 2010:2=1005 nên ta chia A làm ngoặc 2 số liên tiếp

<=> A= \(\left(2^1+2^2\right)+\left(2^3+2^4\right)+.\ldots+\left(2^{2019}+2^{2010}\right)\)

\(A=2\left(2+1\right)+2^3\left(2+1\right)+\cdots+2^{2019}\left(2+1\right)\)

\(A=2\cdot3+2^3\cdot3+\cdots+2^{2019}\cdot3\)

\(A=3\left(2^1+2^3+\cdots+2^{2019}\right)\)

=> A⋮3

bài 2:

a) sửa đề: so sánh A với B= \(2^{2011}-1\)

<=> \(2A=2^1+2^2+.\ldots+2^{2011}\)

\(\Rightarrow2A-A=\left(2^1+2^2+.\ldots+2^{2011}\right)-\left(2^0+2^1+\cdots+2^{2010}\right)\)

\(A=2^{2011}-1\)

vậy A=B

b) vì 2019 và 2011 đều> 2010 nên A>B

c) ƯCLN(440,300)=20

=> \(3^{440}=\left(3^{22}\right)^{20}\)

\(5^{300}=\left(5^{15}\right)^{20}\)

mà ta có: \(3^{22}=3^2\cdot3^{20}=9\cdot\left(3^4\right)^5=9\cdot81^5\)

\(5^{15}=\left(5^3\right)^5=125^5\)

vì \(9\cdot81^5>125^5\)

=> A>B

bài 3:

d) xy+3x-7y=21

xy+3x-7y-21=0

x(y+3)-7(y+3)=0

(y+3)(x-7)=0

=> x=7 và y=-3

bài 4:

=> \(A^2=ab-bc-ca+bc\)

\(A^2=ab-ca\)

\(A^2=a\left(b-c\right)=-20\cdot-5=100\)

TH1: A=10

TH2: A=-10

a, 1/2x +3/5(x-2)=3

    1/2x +3/5.x -3/5.2=3

   (1/2+3/5).x-6/5=3

   11/10.x=21/5

  x=42/11

b,| 1/2x-3/2|= 1/2

=> 1/2x-3/2=1/2

   hoac 1/2x-3/2=-1/2

=> 1/2x=2

hoac 1/2x=1

=> x=4 hoac x=2