4. Сократите: 1) (12 · 21)/(35 · 15); 2) (72 · 11)/(33 · 30); 3) (25 · 17 · 44)/(51 · 8 · 75); 4) (8 · 3 + 8 · 23)/(3 · 16); 5) (17 · 48)/(17 · 16 − 9 · 16); 6) (14 · 5 − 14 · 3)/(21 · 9 + 21 · 3).

1. \(\dfrac{12\cdot21}{35\cdot15}=\dfrac{12}{25}\).
2. \(\dfrac{72\cdot11}{33\cdot30}=\dfrac{4}{5}\).
3. \(\dfrac{25\cdot17\cdot44}{51\cdot8\cdot75}=\dfrac{11}{18}\).
4. \(\dfrac{8\cdot3+8\cdot23}{3\cdot16}=\dfrac{8(3+23)}{48}=\dfrac{13}{3}\).
5. \(\dfrac{17\cdot48}{17\cdot16-9\cdot16}=\dfrac{17\cdot48}{16(17-9)}=\dfrac{51}{8}\).
6. \(\dfrac{14\cdot5-14\cdot3}{21\cdot9+21\cdot3}=\dfrac{14(5-3)}{21(9+3)}=\dfrac{1}{9}\).

Ответ: 1) \(\dfrac{12}{25}\); 2) \(\dfrac{4}{5}\); 3) \(\dfrac{11}{18}\); 4) \(\dfrac{13}{3}\); 5) \(\dfrac{51}{8}\); 6) \(\dfrac{1}{9}\).