Write the expressions: 1. 18 + 9, 27 + 9, ..., 81 + 9; 2. 72 - 9, ..., 9 - 9.

Решение:

1. \( 18+9, 27+9, 36+9, 45+9, 54+9, 63+9, 72+9, 81+9 \)
2. \( 72-9, 63-9, 54-9, 45-9, 36-9, 27-9, 18-9, 9-9 \)

Ответ: 1. \( 18+9, 27+9, 36+9, 45+9, 54+9, 63+9, 72+9, 81+9 \); 2. \( 72-9, 63-9, 54-9, 45-9, 36-9, 27-9, 18-9, 9-9 \).