Câu 2:\(\dfrac{-3}{11}\cdot\dfrac{5}{7}+\dfrac{-5}{7}\cdot\dfrac{8}{11}+2\dfrac{5}{7}\)
\(=\dfrac{-3}{11}\cdot\dfrac{5}{7}+\dfrac{5}{7}\cdot\dfrac{-8}{11}+2+\dfrac{5}{7}\)
\(=\dfrac{5}{7}\cdot\left(\dfrac{-3}{11}+\dfrac{-8}{11}+1\right)+2\)
\(=\dfrac{5}{7}\cdot\left(\dfrac{-11}{11}+1\right)+2\)
\(=\dfrac{5}{7}\cdot0+2\)
\(=2\)
Câu 3:
\(\dfrac{1}{3}< \dfrac{9}{x}< \dfrac{1}{2}\)
+) \(\dfrac{1}{3}< \dfrac{9}{x}\Rightarrow x< 9\cdot3\Rightarrow x< 27\) (1)
+) \(\dfrac{9}{x}< \dfrac{1}{2}\Rightarrow x>9\cdot2\Rightarrow x>18\) (2)
Từ (1) và (2) ta có:
\(18< x< 27\)
Các số nguyên x thỏa mãn là:
\(x\in\left\{19;20;21;22;23;24;25;26\right\}\)
