Объяснение:
(у-2/7)²=9/49
у2+4/49 - 4/7y =9/49
y2 - 4/7y -5/49= 0
Пусть у = t, тогда
t2 - 4/7t - 5/49 =0
D = 16/49 - 4 * (-5/49)= 16/49+20/49 = 36/49
t1 = 6/7 + 4/7 / 2 = 5/7
t2 = 4/7 - 6/7 / 2 = -1/7
y = 5/7 или y =-1/7
