Решите 2/7+5/14; 4/4-3/8; 4/9+1/12

Решим примеры, приводя дроби к общему знаменателю:

1) 2/7 + 5/14 = (2 * 2) / (7 * 2) + 5/14 = 4/14 + 5/14 = (4 + 5) / 14 = 9/14;

2) 4/4 - 3/8 = (4 * 2) / (4 * 2) - 3/8 = 8/8 - 3/8 = (8 - 3) / 8 = 5/8;

3) 4/9 + 1/12 = (4 * 4) / (9 * 4) + (1 * 3) / (12 * 3) = 16/36 + 3/36 = (16 + 3) / 36 = 19/36.

Для примера решим ещё несколько подобных примеров:

1) 1/2 + 5/6 = (1 * 3) / (2 * 3) + 5/6 = 3/6 + 5/6 = (3 + 5) / 6 = 8/6 = (4 * 2) / (3 * 2) = 4/3 = 1 1/3;

2) 2/3 + 1/9 = (2 * 3) / (3 * 3) + 1/9 = 6/9 + 1/9 = (6 + 1) / 9 = 7/9.