\(2:\dfrac{2}{3}-\dfrac{1}{7}=3-\dfrac{1}{7}=\dfrac{20}{7}\)

\(\left(9\dfrac{3}{8}+11\dfrac{5}{7}\right)-\left(5\dfrac{3}{8}+4\dfrac{5}{7}\right)\\ =9+\dfrac{3}{8}+11+\dfrac{5}{7}-5-\dfrac{3}{8}-4-\dfrac{5}{7}\\ =\left(9-5-4\right)+\left(\dfrac{3}{8}-\dfrac{3}{8}\right)+\left(\dfrac{5}{7}-\dfrac{5}{7}\right)+11\\ =0+0+0+11\\ =11\)

1/ \(\left(0,2\right)^{10}:\left(0,2\right)^8=\left(0,2\right)^{10-8}=\left(0,2\right)^2=0,04\)

2/ \(\left(-\dfrac{4}{5}\right)^9:\left(-\dfrac{4}{5}\right)^7=\left(-\dfrac{4}{5}\right)^{9-7}=\left(-\dfrac{4}{5}\right)^2=\dfrac{16}{25}\)

3/ \(\left(\dfrac{2}{3}\right)^{12}:\left(\dfrac{8}{27}\right)^4=\left(\dfrac{2}{3}\right)^{12}:\left(\left(\dfrac{2}{3}\right)^3\right)^4=\left(\dfrac{2}{3}\right)^{12}:\left(\dfrac{2}{3}\right)^{12}=1\)

\(231+\dfrac{x}{15}-46=170\\ \dfrac{x}{15}=170+46-231\\ \dfrac{x}{15}=-15\\ x=-225\)

\(4x+\dfrac{5}{7}x-4x=-\dfrac{15}{7}\\ \dfrac{5}{7}x=-\dfrac{15}{7}\\ x=-3\)

\(\left(5+2x^2\right)\left(x+\dfrac{17}{21}\right)=0\)

\(\Rightarrow x+\dfrac{17}{21}=0\) (do \(5+2x^2>0\))

\(\Rightarrow x=-\dfrac{17}{21}\)

\(4\times x+28+2\times x=88\\ 6\times x=60\\ x=10\)