(x+3)^2+(x-4)^2=2(4-x)(x+3)

(x + 3)^2 + (x - 4)^2 = 2(4 - x)(x + 3)
(x + 3)^2 - 2(4 - x)(x + 3) + (x - 4)^2 = 0
((x + 3) + (x - 4))^2 = 0
(x + 3 + x - 4)^2 = 0
(2x - 1)^2 = 0
2x - 1 = 0
2х = 1
х = 1/2
х = 0,5

Ответ: 0,5.