1)
a) \(89-\left(73-x\right)=20\)
\(\Leftrightarrow73-x=89-20\)
\(\Leftrightarrow73-x=69\)
\(\Leftrightarrow x=73-69\)
\(\Leftrightarrow x=4\)
Vậy \(x=4\)
b) \(\left(x+7\right)-25=13\)
\(\Leftrightarrow x+7=13+25\)
\(\Leftrightarrow x+7=38\)
\(\Leftrightarrow x=38-7\)
\(\Leftrightarrow x=31\)
Vậy \(x=31\)
c) \(140:\left(x-8\right)=7\)
\(\Leftrightarrow x-8=140:7\)
\(\Leftrightarrow x-8=20\)
\(\Leftrightarrow x=20+8\)
\(\Leftrightarrow x=28\)
Vậy \(x=28\)
d) \(6x+x=5^{11}:5^9+3^1\)
\(\Leftrightarrow7x=5^{11}:5^9+3^1\)
\(\Leftrightarrow7x=5^{11-9}+3^1\)
\(\Leftrightarrow7x=5^2+3^1\)
\(\Leftrightarrow7x=25+3\)
\(\Leftrightarrow7x=28\)
\(\Leftrightarrow x=28:7\)
\(\Leftrightarrow x=4\)
Vậy \(x=4\)
e) \(4^x=64\)
\(\Leftrightarrow4^x=4^3\)
\(\Leftrightarrow x=3\)
Vậy \(x=3\)
g) \(9^{x-1}=9\)
\(\Leftrightarrow9^{x-1}=9^1\)
\(\Leftrightarrow x-1=1\)
\(\Leftrightarrow x=1+1\)
\(\Leftrightarrow x=2\)
Vậy \(x=2\)
