Question

Tìm x ,biết :

a) (1/2 - x )³=1/8

b) 5^x+1 - 5^x = 500

 

Answer 1

a) \(\left(\frac{1}{2}-x\right)^3=\frac{1}{8}\Leftrightarrow\left(\frac{1}{2}-x\right)^3=\left(\frac{1}{2}\right) ^3\)

\(\Leftrightarrow\frac{1}{2}-x=\frac{1}{2}\Leftrightarrow x=\frac{1}{2}-\frac{1}{2}=0\)

b) \(5^{x+1}-5^x=500\Leftrightarrow5^x.5^1-5^x=500\)

\(\Leftrightarrow5^x\left(5-1\right)=500\Leftrightarrow5^x.4=500\)

\(\Leftrightarrow5^x=\frac{500}{4}=125=5^3\).Từ đó ta có: \(5^x=5^3\Leftrightarrow x=3\)