Question

calculati ultmia cifra a numarului 16²⁰¹⁹+17²⁰¹⁹+18²⁰²⁰+19²⁰¹⁹+20²⁰²⁰​

Answer 1

Răspuns:

$u( {16}^{2019} ) = 6$

$u( {17}^{2019} ) =3 \\ {17}^{1} = 17 \\ {17}^{2} = 289 \\ {17}^{3} = 4913 \\ {17}^{4} = ...1 \\ {17}^{5} = ...7 \: \\ = > 2019 \div 4 = 504 \: rest \: 3$

$u( {18}^{2020} ) = 6\\ {18}^{1} = 18 \\ {18}^{2} = 324 \\ {18}^{3} = ...2 \\ {18}^{4} = ...6 \\ {18}^{5} = ...8 \: \\ = > 2020 \div 4 = 505 \: rest \: 0$

$u( {19}^{2019} ) = 9\\ {19}^{1} = 19 \\ {19}^{2} = 361 \\ {19}^{3} = ...9 \\ = > 2019 \div 2 = 1009 \: rest \: 1$

$u( {20}^{2020} ) = 0$

$u(suma) = 6 + 3 + 6 + 9 + 0 = 24 \: = > 4$