={0;1;2;3;4;5;6;7;8;9}
={x∈N|x<10}
(101-1):4+1=26(số)
Tổng là (1+101)*26/2=1326
AB=AC
góc A chung
=>ΔADB=ΔAEC
=>AD=AE
1. an onion
2. corn
3. breath
4. armchair
5. February