1. Проверь, верны ли равенства. 13. (10+2) = 13・10+13・2 15.(102) = 15・10・2 2. (990-90):100. 990-40+25・7・4 (20 + 5). 4=20+5 72:(8.3)=72:8 1000:(1000・1) - 1 12.5+ (84-72:3)

1. Проверка равенств:

• Первое равенство: 13 ⋅ (10 + 2) = 13 ⋅ 10 + 13 ⋅ 2

Левая часть: 13 ⋅ (10 + 2) = 13 ⋅ 12 = 156

Правая часть: 13 ⋅ 10 + 13 ⋅ 2 = 130 + 26 = 156

Так как 156 = 156, то равенство верное.

• Второе равенство: 15 ⋅ (10 ⋅ 2) = 15 ⋅ 10 ⋅ 2

Левая часть: 15 ⋅ (10 ⋅ 2) = 15 ⋅ 20 = 300

Правая часть: 15 ⋅ 10 ⋅ 2 = 150 ⋅ 2 = 300

Так как 300 = 300, то равенство верное.

2. Вычисление выражений:

• (990 - 90) : 100 ⋅ 9

(990 - 90) : 100 ⋅ 9 = 900 : 100 ⋅ 9 = 9 ⋅ 9 = 81

• 990 - 40 + 25 ⋅ 7 ⋅ 4

990 - 40 + 25 ⋅ 7 ⋅ 4 = 990 - 40 + 25 ⋅ 28 = 990 - 40 + 700 = 950 + 700 = 1650

• (20 + 5) ⋅ 4 = 20 + 5

Левая часть: (20 + 5) ⋅ 4 = 25 ⋅ 4 = 100

Правая часть: 20 + 5 = 25

Равенство неверное, так как 100 ≠ 25.

• 72 : (8 ⋅ 3) = 72 : 8 ⋅ 3

Левая часть: 72 : (8 ⋅ 3) = 72 : 24 = 3

Правая часть: 72 : 8 ⋅ 3 = 9 ⋅ 3 = 27

Равенство неверное, так как 3 ≠ 27.

• 1000 : (1000 ⋅ 1) - 1

1000 : (1000 ⋅ 1) - 1 = 1000 : 1000 - 1 = 1 - 1 = 0

• 12 ⋅ 5 + (84 - 72 : 3)

12 ⋅ 5 + (84 - 72 : 3) = 12 ⋅ 5 + (84 - 24) = 60 + 60 = 120