(5x - 1)^2 - 16x^2 = 0
(5x - 1 - 4x)(5x - 1 + 4x) = 0
(x - 1)(9x - 1) = 0
x - 1 = 0
x = 1
9x - 1 = 0
9x = 1
x = 1/9
==================================
x^2 + 6x + 9 + x^2 - 8x + 16 = 2(4x + 12 - x^2 - 3x)
2x^2 - 2x + 25 = 2(x + 12 - x^2)
2x^2 - 2x + 25 = 2x + 24 - 2x^2
4x^2 - 4x + 1 = 0
(2x - 1)^2 = 0
2x - 1 = 0
2x = 1
x = 1/2 = 0,5