2 x 5² - 5 x [ 3² + 5 - 3 x ( 2 y - 2004⁰ ) ] = 5²
2 x 25 - 5 x [ 9 + 5 - 3 x ( 2 y - 1 ) ] = 25
5 x [ 14 - 3 x ( 2 y - 1 ) ] = 50 - 25
5 x [ 14 - 3 x ( 2 y - 1 ) ] = 25
14 - 3 x ( 2 y - 1 ) = 25 : 5
3 x ( 2 y - 1 ) = 14 - 5 = 9
2 y - 1 = 9 : 3
2 y - 1 = 3
2 y = 3 + 1
y = 4 : 2
y = 2 → numarul necunoscut