Đáp án:
a.$U(30)=\{1, 2, 3, 5, 6, 10, 15, 30\}$
b.$U(225)=\{1, 3, 5, 9, 15, 25, 45, 75, 225\}$
c.$U(210)=\{1, 2, 3, 5, 6, 7, 10, 14, 15, 21, 30, 35, 42, 70, 105, 210\}$
d.$U(242)=\{1, 2, 11, 22, 121, 242\}$
Giải thích các bước giải:
a.Ta có:
$30=2\cdot 3\cdot 5$
$\to U(30)=\{1, 2, 3, 5, 6, 10, 15, 30\}$
b.Ta có:
$225=3^2\cdot 5^2$
$\to U(225)=\{1, 3, 5, 9, 15, 25, 45, 75, 225\}$
c.Ta có:
$210=2\cdot 3\cdot 5\cdot 7$
$\to U(210)=\{1, 2, 3, 5, 6, 7, 10, 14, 15, 21, 30, 35, 42, 70, 105, 210\}$
d.Ta có:
$242=2\cdot 11^2$
$\to U(242)=\{1, 2, 11, 22, 121, 242\}$
