Уравнение: 2/3-(x + 1/21)=2/7
2/3-(x + 1/21)=2/7
х+1/21=2/3-2/7
х+1/21=14/21-6/21
х+1/21=8/21
х=8/21-1/21
х=7/21
х=1/3
Ответ:1/3
2/3 - ( Х + 1/21 ) = 2/7 Х + 1/21 = 2/3 - 2/7 2/3 - 2/7 = 14/21 - 6/21 = 8/21 Х + 1/21 = 8/21 Х = 8/21 - 1/21 Х = 7/21 Х = 1/3