7 Реши уравнения с комментированием и проверкой: a) 115 - 6 ⋅ x = 73 в) 18 + (16 – x) ⋅ 8 = 90 б) 540 : x + 85 = 91 г) (4900 : у – 280) : 60 = 7

Ответ: a) x=7, б) x=90, в) x=7, г) y=700

1. a) 115 - 6 ⋅ x = 73
   • 6 ⋅ x = 115 - 73
   • 6 ⋅ x = 42
   • x = 42 : 6
   • x = 7

   Проверка: 115 - 6 ⋅ 7 = 115 - 42 = 73

2. б) 540 : x + 85 = 91
   • 540 : x = 91 - 85
   • 540 : x = 6
   • x = 540 : 6
   • x = 90

   Проверка: 540 : 90 + 85 = 6 + 85 = 91

3. в) 18 + (16 – x) ⋅ 8 = 90
   • (16 – x) ⋅ 8 = 90 - 18
   • (16 – x) ⋅ 8 = 72
   • 16 – x = 72 : 8
   • 16 – x = 9
   • x = 16 - 9
   • x = 7

   Проверка: 18 + (16 – 7) ⋅ 8 = 18 + 9 ⋅ 8 = 18 + 72 = 90

4. г) (4900 : у – 280) : 60 = 7
   • 4900 : у – 280 = 7 ⋅ 60
   • 4900 : у – 280 = 420
   • 4900 : у = 420 + 280
   • 4900 : у = 700
   • у = 4900 : 700
   • у = 700

   Проверка: (4900 : 700 – 280) : 60 = (7 - 280) : 60 = 420 : 60 = 7

Ответ: a) x=7, б) x=90, в) x=7, г) y=700