Ex 10: Reanrrange these words to make meaningful sentences 1.often/Lan/with the work/her parents/helps/. 2. a student/at/Nam/a specialized school/is/. 3.you/every day/do/go to school/How/? 4.that/store/a lot of/There/interesting things/in/. 5.It/the suburbs/is/in/a small village/. 6.very/Is/intelligent/your friend/? 7.teacher/dark/has/our/hair/straight/long/.

Cho D=3²+3⁴+3⁶+...+3¹²⁰.Chứng minh rằng: a)D chia hết cho 3 b)D chia hết cho 91