РЕШЕНИЕ:
(x2−69)2+(x2 + 4x−21)2=0
x2 + 4x − 12 = 0
D = 42 - 4∙1∙(-12) = 16 + 48 = 64 = 82
x1 = (- 4 + 8) / 2 = 4/2 = 2
x1 = (- 4 - 8) / 2 = - 12/2 = -6
x2+ 4x−12 = (x+6)(x-2)
(x2−69)2+(x2 + 4x−12)2=0
((x-6)(x+6))2+(x+6)2 (x-6)2=0
(x-6)2(x+6)2 +(x+6)2 (x-2)2=0
(x+6)2((x-6)2 +(x-2)2)=0
(x-6)2 +(x-2)2 ≠ 0
x+6 = 0
x = - 6
Ответ: - 6