12^x+3*(4^x-3^x-1)-3=0

12^x + 3 * (4^x - 3^x - 1) - 3 = 0;

3 * (4^x - 3^x - 1) = (3 * 4^x) - (3 * 3^x) - (3 * 1) = 12^x - 9^x - 3 = 3^x - 3;

12^x + 3 * (4^x - 3^x - 1) - 3 = 12^x + 3^x - 3 - 3 = 0; : 3;

4^x + 1^x - 2 = 0;

1^x = 1;

4^x + 1 - 2 = 0;

4^x - 1 = 0;

4^x = 1;

x = 0:

4^0 = 1.

Ответ: х = 0.