Question

Tìm x thuộc N , biết

a) ( 4x + 5 ) : 3 - 121 : 11 = 4

b) 1 + 3 + 5 .... + x = 1600 ( x là số lẻ )

c) ( 2x + 1 )³ =125

d) (4x - 1 )² = 259

e) 2^x . 2^x+3 = 144

g) 3^2x+2 = 9^x+3

Answer 1

a) \(\left(4x+5\right):3-121:11=4\)

\(\Leftrightarrow\left(\dfrac{4x}{3}+\dfrac{5}{3}\right)-11=4\)

\(\Leftrightarrow\dfrac{4x}{3}+\dfrac{5}{3}-11=4\)

\(\Leftrightarrow\dfrac{4x}{3}+\dfrac{5}{3}-\dfrac{33}{3}=4\)

\(\Leftrightarrow\dfrac{4x}{3}+\dfrac{5-33}{3}=4\)

\(\Leftrightarrow\dfrac{4x}{3}-\dfrac{28}{3}=4\)

\(\Leftrightarrow\dfrac{4x}{3}=4+\dfrac{28}{3}\)

\(\Leftrightarrow\dfrac{4x}{3}=\dfrac{12}{3}+\dfrac{28}{3}\)

\(\Leftrightarrow\dfrac{4x}{3}=\dfrac{12+28}{3}\)

\(\Leftrightarrow\dfrac{4x}{3}=\dfrac{40}{3}\)

\(\Leftrightarrow4x=\dfrac{40}{3}.3\)

\(\Leftrightarrow4x=40\)

\(\Leftrightarrow x=\dfrac{40}{4}=10\)

Vậy \(x=10\)

Answer 2

c) ( 2x + 1 )³ =125

=> (2x+1)³=5³

=> 2x+1=5

=> 2x=4

=> x=2

vậy x=2