2:
a: \(\dfrac{7}{23}\cdot\left[-\dfrac{8}{6}-\dfrac{45}{18}\right]\)
\(=\dfrac{7}{23}\left(-\dfrac{4}{3}-\dfrac{5}{2}\right)\)
\(=\dfrac{7}{23}\cdot\dfrac{-4\cdot2-5\cdot3}{6}\)
\(=\dfrac{7}{6}\cdot\dfrac{-23}{23}=-\dfrac{7}{6}\)
b: \(12,5\left(-\dfrac{5}{7}\right)+1,5\left(-\dfrac{5}{7}\right)\)
\(=-\dfrac{5}{7}\left(12,5+1,5\right)\)
\(=-\dfrac{5}{7}\cdot14=-10\)
c: \(\dfrac{3^{2014}\cdot8^{19}}{6^{60}\cdot3^{1955}}\)
\(=\dfrac{3^{2014}\cdot2^{57}}{2^{60}\cdot3^{2015}}=\dfrac{1}{2^3\cdot3}=\dfrac{1}{24}\)
3:
a: \(\left(\dfrac{2}{3}\right)^x=\dfrac{8}{27}\)
=>\(\left(\dfrac{2}{3}\right)^x=\left(\dfrac{2}{3}\right)^3\)
=>x=3
b: \(\dfrac{2}{5}x-\dfrac{1}{3}=\dfrac{3}{4}\)
=>\(x\cdot\dfrac{2}{5}=\dfrac{3}{4}+\dfrac{1}{3}=\dfrac{9+4}{12}=\dfrac{13}{12}\)
=>\(x=\dfrac{13}{12}:\dfrac{2}{5}=\dfrac{13}{12}\cdot\dfrac{5}{2}=\dfrac{65}{24}\)
4:
MQ=BC=4cm
Diện tích xung quanh là:
\(\left(4+5\right)\cdot2\cdot7=14\cdot9=126\left(cm^2\right)\)
Thể tích hình hộp chữ nhật là:
\(4\cdot5\cdot7=20\cdot7=140\left(cm^3\right)\)
