Question

Calculați ultima cifră a numărului 7²⁰²¹ dau Coroana si 20 de puncte. Am nevoie urgent de un raspuns!!​

Answer 1

$U(7^{2021}) = U(7^{2020}\cdot 7) \\=U(7^{4\cdot 505}\cdot 7) \\= U\big[(7^{4})^{505}\cdot 7)\big] \\ =U\big[(7^2\cdot 7^2)^{505}\cdot 7\big]\\ =U(9\cdot 9)^{505}\cdot 7\\ = U(81^{505}\cdot 7)\\= U(1^{505}\cdot 7)\\ = 7$