Question

Bài 2:Tìm x biết :

a)\(2^{x+2}-2^x=96\)                       b) \(7^{x+2}+2.7^{x-1}=345\)

Answer 1

a) 2^{x + 2} - 2^x = 96

=> 2^x . 4 - 2^x = 96

=> 2^x . (4 - 1) = 96

=> 2^x . 3 = 96

=> 2^x = 96 : 3

=> 2^x = 32

=> 2^x = 2⁵

=> x = 5

Answer 2

a) 2^{x + 2} - 2^x = 96

=> 2^x. 2² - 2^x = 96

=> 2^x( 4 - 1 ) = 96

=> 2^x = 96 : 3

=> 2^x = 2⁵

=> x = 5

Answer 3

b) 7^{x + 2} + 2 . 7^{x - 1} = 345

=> 7^{x - 1} . ( 7³ + 2 ) = 345

=> 7^{x - 1} . 345 = 345

=> 7^{x - 1} = 345 : 345

=> 7^{x - 1} = 1 = 7⁰

=> x - 1 = 0

=> x = 1

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Answer 4

                                                            Bài giải

a, \(2^{x+2}-2^x=96\)

\(2^x\left(2^2-1\right)=96\)

\(2^x\cdot3=96\)

\(2^x=96\text{ : }3\)

\(2^x=32\)

\(2^x=2^5\)

\(\Rightarrow\text{ }x=5\)

b, \(7^{x+2}+2\cdot7^{x-1}=345\)

\(7^{x-1}\left(7^3+2\right)=345\)

\(7^{x-1}\cdot345=345\)

\(7^{x-1}=345\text{ : }345\)

\(7^{x-1}=1\)

\(7^{x-1}=7^0\)

\(\Rightarrow\text{ }x-1=0\)

\(x=1\)

Answer 5

                                                            Bài giải

a, \(2^{x+2}-2^x=96\)

\(2^x\left(2^2-1\right)=96\)

\(2^x\cdot3=96\)

\(2^x=96\text{ : }3\)

\(2^x=32\)

\(2^x=2^5\)

\(\Rightarrow\text{ }x=5\)

b, \(7^{x+2}+2\cdot7^{x-1}=345\)

\(7^{x-1}\left(7^3+2\right)=345\)

\(7^{x-1}\cdot345=345\)

\(7^{x-1}=345\text{ : }345\)

\(7^{x-1}=1\)

\(7^{x-1}=7^0\)

\(\Rightarrow\text{ }x-1=0\)

\(x=1\)

Answer 6

            Bài làm :

 \(a\text{)}2^{x+2}-2^x=96\)

\(\Leftrightarrow2^x\left(2^2-1\right)=96\)

\(\Leftrightarrow2^x.3=96\)

\(\Leftrightarrow2^x=96\div3\)

\(\Leftrightarrow2^x=32\)

\(\Leftrightarrow2^x=2^5\)

\(\Leftrightarrow\text{ }x=5\)

 \(b\text{)}7^{x+2}+2.7^{x-1}=345\)

\(\Leftrightarrow7^{x-1}\left(7^3+2\right)=345\)

\(\Leftrightarrow7^{x-1}.345=345\)

\(\Leftrightarrow7^{x-1}=345\text{ }\div345\)

\(\Leftrightarrow7^{x-1}=1\)

\(\Leftrightarrow7^{x-1}=7^0\)

\(\Leftrightarrow\text{ }x-1=0\)

\(\Leftrightarrow x=1\)