Question

Tìm số tự nhiên x, biết:
a, 13 - x² = 4
b, ( 2x - 4 )3 = 8
c, 2 + 18 : 3^x = 4
d, 2^x + 2^{x + 3} = 144
Giải chi tiết ( mik đang cần gấp ạ )
 

Answer 1

a) 13 - x² = 4

x² = 13 - 4

x² = 9

x = 3 (nhận) hoặc x = -3 (loại)

Vậy x = 3

b) Sửa đề

(2x - 4)³ = 8

(2x - 4)³ = 2³

2x - 4 = 2

2x = 2 + 4

2x = 6

x = 6 : 2

x = 3

c) 2 + 18 : 3^x  = 4

28 : 3^x = 4 - 2

18 : 3^x = 2

3^x = 18 : 2

3^x = 9

3^x = 3²

x = 2

d) 2^x + 2^(x + 3) = 144

2^x.(1 + 2³) = 144

2^x . 9 = 144

2^x = 144 : 9

2^x = 16

2^x = 2⁴

x = 4

Answer 2

a)

x^2=9

=> x=3 hoặc x=-3

b)

2x-4=8/3

2x=20/3

x=10/3

=> x=\(\varnothing\)

c)

18:3^x=2

3^x=9

=> x=2

d)

2^x+2^x*2^3=144

2^x(1+8)=144

2^x*9=144

2^x=16

=> x=4

Answer 3

\(13-x^2=4\)

=>\(13-x^2-4=0\)

=>\(9-x^2=0\)

=>x=3

(2x-4)3=8

=>2x-4\(=8:3=\dfrac{8}{3}\)

=>2x=\(\dfrac{8}{3}+4=\dfrac{20}{3}\)

=>x\(=\dfrac{10}{3}\)

2+18:\(3^x\)=4

=>\(18:3^x=4-2=2\)

=>\(3^x=18:2=9\)

=>x=2

 

Answer 4

`13-x^2 = 4`

`x^2=13-4`

`x^2 = 9`

`=>`\(x^2=\left(\pm3\right)^2\)

`=>x={-3;3}`

`(2x-4)^3=8`

`(2x-4)^3=2^3`

`2x-4=2`

`2x=6`

`x=3`

`2+18:3^x=4`

`18:3^x = 4-2`

`18:3^x = 2`

`3^x = 18:2`

`3^x = 9`

`=>x=2`

`2^x +2^(x+3)=144`

`2^x +2^x . 2^3 = 144`

`2^x +2^x . 8 = 144`

`2^x . (8+1)=144`

`2^x.9=144`

`2^x = 144:9`

`2^x = 16`

`=> x = 4`