Bài 1.
a) \(\dfrac{2}{3}\cdot\dfrac{1}{2}+\dfrac{5}{6}\cdot\left(-\dfrac{2}{5}\right)\)
\(=\dfrac{1}{3}+\left(-\dfrac{1}{3}\right)\)
\(=0\)
b) \(\left(\dfrac{3}{4}+0,25\right):\dfrac{1}{6}\)
\(=\left(0,75+0,25\right)\cdot6\)
\(=1\cdot6\)
\(=6\)
c) \(\sqrt{0,81}+\sqrt{\dfrac{1}{100}}\)
\(=\sqrt{0,9^2}+\sqrt{\left(\dfrac{1}{10}\right)^2}\)
\(=0,9+\dfrac{1}{10}\)
\(=0,9+0,1\)
\(=1\)
Bài 2.
a) \(\dfrac{x}{25}=\dfrac{2}{5}\)
\(\Rightarrow x=\dfrac{2}{5}\cdot25\)
\(\Rightarrow x=10\)
b) \(\left(\dfrac{1}{3}\right)^{x-1}+\dfrac{1}{9}=\dfrac{10}{81}\)
\(\Rightarrow\left(\dfrac{1}{3}\right)^{x-1}=\dfrac{10}{81}-\dfrac{1}{9}\)
\(\Rightarrow\left(\dfrac{1}{3}\right)^{x-1}=\dfrac{1}{81}\)
\(\Rightarrow\left(\dfrac{1}{3}\right)^{x-1}=\left(\dfrac{1}{3}\right)^4\)
\(\Rightarrow x-1=4\)
\(\Rightarrow x=4+1\)
\(\Rightarrow x=5\)
\(\text{#}Toru\)
