1. 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).

Сократим дроби, разложив числители и знаменатели на множители.

1. \(\dfrac{12\cdot21}{35\cdot15}=\dfrac{12\cdot3}{5\cdot15}=\dfrac{12}{25}\).
2. \(\dfrac{72\cdot11}{33\cdot30}=\dfrac{72}{3\cdot30}=\dfrac{72}{90}=\dfrac45\).
3. \(\dfrac{25\cdot17\cdot44}{51\cdot8\cdot75}=\dfrac{1\cdot1\cdot44}{3\cdot3\cdot8}=\dfrac{44}{72}=\dfrac{11}{18}\).
4. \(\dfrac{8\cdot3+8\cdot23}{3\cdot16}=\dfrac{8(3+23)}{3\cdot16}=\dfrac{8\cdot26}{48}=\dfrac{13}{3}\).
5. \(\dfrac{17\cdot48}{17\cdot16-9\cdot16}=\dfrac{17\cdot48}{16(17-9)}=\dfrac{17\cdot48}{16\cdot8}=\dfrac{51}{8}\).
6. \(\dfrac{14\cdot5-14\cdot3}{21\cdot9+21\cdot3}=\dfrac{14(5-3)}{21(9+3)}=\dfrac{14\cdot2}{21\cdot12}=\dfrac19\).

Ответ: 1) \(\dfrac{12}{25}\); 2) \(\dfrac45\); 3) \(\dfrac{11}{18}\); 4) \(\dfrac{13}{3}\); 5) \(\dfrac{51}{8}\); 6) \(\dfrac19\).