Question

Ultima cifra 5²⁰¹⁹= 5 nu?
că orice Nr 5⁸⁹ = 5 pt că 5 n =5
​

Answer 1

$5¹=5\\5²=25\\\dots \\\dots\\\dots\\u(5 {}^{n} ) = mereu \: \: 5 \\ \\ \iff \: u(5 {}^{2019} ) = 5$