Solution:
Apply C_{2} → C_{2} - C_{1}
It becomes,
(2 ^ x + 2 ^ (- x)) ^ 2 - (2 ^ x - 2 ^ (- x)) ^ 2
It is based tn (a + b) ^ 2 - (a - b) ^ 2 = 4ab
4ab = 4.2 ^ x * 2 ^ (- x)
the discriminant will change into

Lake 4 common of + o that two root same. Hence it will become 0.