№4. Решите уравнение: a) -40 \(\cdot\) (-7x + 5) = -1600; б) (-20x - 50) \(\cdot\) 2 = 100; в) 2,1 \(\cdot\) (4 - 6y) = -42; г) -3 \(\cdot\) (2 - 15x) = -6.

Решение:

1. а) \( -40 \cdot (-7x + 5) = -1600 \)
   \( -7x + 5 = \frac{-1600}{-40} \)
   \( -7x + 5 = 40 \)
   \( -7x = 40 - 5 \)
   \( -7x = 35 \)
   \( x = \frac{35}{-7} \)
   \( x = -5 \)
2. б) \( (-20x - 50) \cdot 2 = 100 \)
   \( -20x - 50 = \frac{100}{2} \)
   \( -20x - 50 = 50 \)
   \( -20x = 50 + 50 \)
   \( -20x = 100 \)
   \( x = \frac{100}{-20} \)
   \( x = -5 \)
3. в) \( 2,1 \cdot (4 - 6y) = -42 \)
   \( 4 - 6y = \frac{-42}{2,1} \)
   \( 4 - 6y = -20 \)
   \( -6y = -20 - 4 \)
   \( -6y = -24 \)
   \( y = \frac{-24}{-6} \)
   \( y = 4 \)
4. г) \( -3 \cdot (2 - 15x) = -6 \)
   \( 2 - 15x = \frac{-6}{-3} \)
   \( 2 - 15x = 2 \)
   \( -15x = 2 - 2 \)
   \( -15x = 0 \)
   \( x = 0 \)

Ответ: а) -5; б) -5; в) 4; г) 0.