Д/З

Решение:

1. \( 3(x-1) - 5(x+9) = 20 \)
   \( 3x - 3 - 5x - 45 = 20 \)
   \( -2x - 48 = 20 \)
   \( -2x = 20 + 48 \)
   \( -2x = 68 \)
   \( x = \frac{68}{-2} \)
   \( x = -34 \)
2. \( 5.5(y-2) - 4(y+9) = -15 \)
   \( 5.5y - 11 - 4y - 36 = -15 \)
   \( 1.5y - 47 = -15 \)
   \( 1.5y = -15 + 47 \)
   \( 1.5y = 32 \)
   \( y = \frac{32}{1.5} = \frac{320}{15} = \frac{64}{3} \)
3. \( 31x - 29 = 20x + 48 \)
   \( 31x - 20x = 48 + 29 \)
   \( 11x = 77 \)
   \( x = \frac{77}{11} \)
   \( x = 7 \)
4. \( 9(x-9.9) - 2(x-8) = 2x \)
   \( 9x - 89.1 - 2x + 16 = 2x \)
   \( 7x - 73.1 = 2x \)
   \( 7x - 2x = 73.1 \)
   \( 5x = 73.1 \)
   \( x = \frac{73.1}{5} = 14.62 \)
5. \( 15(x-8.6) - 5 = 21x \)
   \( 15x - 129 - 5 = 21x \)
   \( 15x - 134 = 21x \)
   \( -134 = 21x - 15x \)
   \( -134 = 6x \)
   \( x = \frac{-134}{6} = \frac{-67}{3} \)

Ответ: a) x = -34; б) y = 64/3; в) x = 7; г) x = 14.62; д) x = -67/3.