1)8x-21=3x+9 2)10-x=12x+40 3)9x-10=x+14 4)3x-7=x+14

Решите задачу:

$1) \: 8x - 21 = 3x + 9 \\ 8x - 3x = 9 + 21 \\ 5x = 30 \\ x = 6$
$2) \: 10 - x = 12x + 40 \\ 12x + x = 10 - 40 \\ 13x = - 30 \\ x = - \frac{30}{13} = - 2 \frac{4}{13}$
$3) \: 9x - 10 = x + 14 \\ 9x - x = 14 + 10 \\ 8x = 24 \\ x = 3$
$4) \: 3x - 7 = x + 14 \\ 3x - x = 14 + 7 \\ 2x = 21 \\ x = \frac{21}{2} = 10 \frac{1}{2}$