Given that a is a root of the equation x2-5x + 1 = 0, then the number of bits of A4 + A-4 is______ .

Given that a is a root of the equation x2-5x + 1 = 0, then the number of bits of A4 + A-4 is______ .

∵ A4 + 1A4 = (A2 + 1A2) 2-2 = [(A2 + 1a) 2-2] 2-2 ①, and ∵ x2 + 1 = 5x, so x2 + 1 = 5x ②, substituting ② into ①, the original formula = [(5xx) 2-2] 2-2 = 527, the number is 7, so the answer is 7