Răspuns:
Explicație pas cu pas:
2.
U(2^1) = 2
U(2^2) = 4
U(2^3) = 8
U(2^4) = 16
U(2^5) = 2
ultima cifra se repeta din 4 in 4
31 : 4 = 7 rest 3
U(2^31) = 8
U(3^1) = 3
U(3^2) = 9
U(3^3) = 7
U(3^4) = 1
U(3^5) = 3
ultima cifra se repeta din 4 in 4
42 : 4 = 10 rest 2
U(3^42) = 9
U(A) = U(8 + 9) = U(17) = 7
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3.
81^17*7^4 = (3^4)^17*7^4 = (3^17)^4*7^4 = [(3^17)^2*7^2]^2 = patrat perfect
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4.
2^9 + 2^10 + 2^11 = n*2^9
2^9*(1 + 2 + 2^2) = n*2^9
2^9*(1 + 2 + 4) = n*2^9
7*2^9 = n*2^9
n = 7
