Question

[Nguyễn Huỳnh Thanh Tâm]

tìm x :

A , 3^x.3=243 

B, 7.2^x = 56

c, x³ = 8²

D, x²⁰ = x

E ,2^x -15 = 17

F, ( 2x +1)³ = 9.81

G, 2.3^x = 162

Answer 1

[Vũ Đức Thịnh]

a) 3x.3 = 243

=> 3x+1 = 35

=> x+1 = 5

=> x = 4

b) 7.2x = 56

=> 2x = 8

=> 2x = 23

=> x = 3

c) x3=82

=> x3 = (23)2

=> x3=26

=> x3 = ( 22 )3

=> x3=43

=> x = 4

d) x20=x

=> x20-x=0

=> x(x19-1)=0

\(\Rightarrow\left[{}\begin{matrix}x=0\\x^{19}-1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x^{19}=1\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=1\end{matrix}\right.\)

e) 2x-15=17

=> 2x=32

=> 2x=25

=> x = 5

f) (2x+1)3 = 9.81

=> (2x+1)3 = 729

=> (2x+1)3 = 93

=> 2x+1 = 9

=> 2x = 8

=> x = 4

g) 2.3x=162

=> 3x = 81

=> 3x = 34

=> x= 4

Answer 2

[Dora]

`a)3^{x}.3=243`

`3^{x}=243:3=81`

`3^{x}=3^4`

`x=4`

____________________________

`b)7.2^{x}=56`

`2^{x}-56:7=8`

`2^{x}=2^{3}`

`x=3`

____________________________

`c)x^3=8^2`

`x^3=64`

`x^3=4^3`

`x=4`

____________________________

`d)x^20=x`

`x^{20}-x=0`

`x(x^{19}-1)=0`

`@TH1:x=0`

`@TH2:x^{19}-1=0=>x^{19}=1=>x=1`

____________________________

`e)2^{x}-15=17`

`2^{x}=17+15=32`

`2^{x}=2^5`

`x=5`

____________________________

`f)(2x+1)^3=9.81`

`(2x+1)^3=9^3`

`2x+1=9`

`2x=8`

`x=4`

____________________________

`g)2.3^x=162`

`3^x=162:2=81`

`3^x=3^4`

`x=4`