Question

Tìm x 

a.   (x-1)³ =125

b.   (2 . x+1)³=343

c.    720 : [41-(2 . x-5)]=2^3.5

Nêu cách giải hộ mình

Answer 1

(x - 1)³ = 125

=> (x - 1)³ = 5³

=> x - 1 = 5

=> x = 5 + 1

=> x = 6

(2x + 1)³ = 343

=> (2x + 1)³ = 7³

=> 2x + 1 = 7

=> 2x = 7 - 1

=> 2x = 6

=>  x = 3

Answer 2

720 : [41 - (2x - 5)] = 2³.5

=> 720:[41 - (2x - 5)] = 40

=> 41 - (2x - 5) = 720 : 40

=> 41 - (2x - 5) = 18

=> 2x - 5 = 41 - 18

=> 2x - 5 = 23

=> 2x = 23 + 5

=> 2x = 28

=> x = 14

Answer 3

a) \(\left(x-1\right)^3=125\)
\(\Rightarrow\left(x-1\right)^3=5^3\)
\(\Rightarrow x-1=5\)
\(\Rightarrow x=5+1=6\)
b) \(\left(2\cdot x+1\right)^3=343\)
\(\Rightarrow\left(2\cdot x+1\right)^3=7^3\)
\(\Rightarrow2\cdot x+1=7\)

\(\Rightarrow2\cdot x=7-1\)

\(\Rightarrow2\cdot x=6\)
\(\Rightarrow x=6:2=3\)
c) \(720:\left[41-\left(2\cdot x-5\right)\right]=2^3\cdot5\)

\(720:\left[41-\left(2\cdot x-5\right)\right]=8\cdot5\)

\(720:\left[41-\left(2\cdot x-5\right)\right]=40\)
\(\Rightarrow41-\left(2\cdot x-5\right)=720:40\)

\(\Rightarrow41-\left(2\cdot x-5\right)=18\)

\(\Rightarrow2\cdot x-5=41-18\)

\(\Rightarrow2\cdot x-5=23\)
=> 2 . x = 23 + 5
=> 2 . x = 28

=> x = 28 : 2 = 14

Answer 4

a) ( x - 1 )³ = 125

=> ( x - 1 )³ = 5³

=> x - 1 = 5

=> x = 6