(х+3)^2+(х-7)^2=2х^2

(a+b)²=a²+2ab+b²
(a-b)²=a²-2ab+b²

(x+3)²+(x-7)²=2x²
x²+6x+9+x²-14x+49=2x²
x²+x²-2x²+6x-14x=-9-49
- 8x= - 58
8x=58
x=7,25