Trong thí nghiệm ion giao thoa ánh sáng khoảng cách giữa 2 khe hẹp là 0,5mm, Khoảng cách từ 2 khe màn quan sát là 2 mét bước sóng ánh sáng là 0,4micromet.

Xác định khoảng vân giao thoa vị trí vân sáng bậc 3 và vân tối 5 kể từ vân trung tâm

cho a, b,c ≥ 0 ; a+b+c=3 cmr 1/(2ab+1) + 1/(2bc+1) + 1/(2ac+1) ≥ 2/(abc+1)

ae giải dễ hiểu hộ tui đc ko

a/b+c=b/a+c=c/a+b.tính a/b+c

tỷ số 2 cạnh của hình chữ nhật là 5/9 biết chu vi bằng 56cm tính diện tích của hình chữ nhật

cho a, b,c ≥ 0 ; a+b+c=3 cmr 1/(2ab+1) + 1/(2bc+1) + 1/(2ac+1) ≥ 2/(abc+1)

  câu 1:Nói trong chuyển động tròn, gia tốc của chất điểm là gia tốc hướng tâm là đúng hay sai? Giải thích.

câu 2 :Tính gia tốc của đầu mút kim giây của một đồng hồ. Chiều dài của kim là 2,5cm.

11/ A: What __________ you __________ (do) at 7 p.m. yesterday?
B: I was eating out with some of my friends.
12/ A magnitude 8 earthquake ________________ (shake) his town abruptly, and then many
houses and public facilities collapsed.
13/ It’s necessary to prepare an emergency kit before a tropical storm ________________
(break).
14/ Ordering fast food, like pizza, via voice messages ________________ (become) popular in
three years.
15/ You can’t meet my boss now. He ________________ (not be) in the head office until next
Tuesday.
16/ Kevin ________________ (translate) a Vietnamese novel for five hours yesterday.
17/ A: Who ________________ (invent) the World Wide Web?
B: Tim Berners-Lee.
18/ I can’t leave the classroom until my teacher ________________ (give) me feedback.
19/ Naomi ________________ (run) around the park when an apple fell on her head.
MARKS
20/ I hope Viet Nam ________________ (be) a powerful country in cyberspace in about 50
years.
21/ My teacher ________________ (say) she was happy to see me become more mature.
22/ While I was telling my child a folk story, my husband ________________ (work) at the
desk.
23/ She found it difficult ________________ (teach) 50 students online.
24/ When I was in primary school, I ________________ (not visit) the city zoo.
25/ At present, my mother ________________ (prepare) some warm clothes for me to go
camping in the forest.
26/ I ________________ (try) to climb the ladder to avoid the flood water at 8 p.m. yesterday.
27/ The rescue team ________________ (find) two survivors in the collapsed building after the
tornado.
28/ A: The play ________________ (start) at 7 p.m. on Monday. Would you like me to book
your ticket in advance?
B: If you wouldn't mind.
29/ I asked my cousin why he ________________ (not like) watching environmental
documentaries.

Câu 10. Chứng minh các bất đẳng thức:

a) (a + b)2 ≤ 2(a2 + b2)

b) (a + b + c)2 ≤ 3(a2 + b2 + c2)

1/ Kate ________________ (not often buy) food and drink in the supermarket. She prefers to
buy them at the open-air market.
2/ While my father ________________ (chop) wood in the back garden, I am slicing beef in
the chicken.
3/ As soon as Peter gathers enough information about the protection of endangered species,
he ________________ (start) doing his wildlife project.
4/ Before I ________________ (leave) home, I turned off the electrical appliances.
5/ A: What __________ you __________ (do) after you browsed around the boutiques?
B: I returned home and watched my favourite TV show.
6/ My father never ________________ (throw) away rubbish in public.
7/ There ________________ (be) bumpy roads when I came back to my hometown.
8/ I ________________ (catch) the bus to my office instead of using my car this morning.
9/ The pilot suddenly saw a volcanic eruption while he ________________ (fly) across
Stromboli, Italy.
10/ We ________________ (drive) home when it began to rain torrentially.

Cho tam giác ABC vuông tại A có AB=3cm AC=4cm. Vẽ phân giác BD (D thuộc AC ), từ D vẽ DE vuông với BC (E thuộc BC) a)cm tam giác ABD=EBD b)Cm DB>DE