Вывод формулы системы линз (d=d1+d2++dn) , учитывая , что линзы тонкие

1my mother is bitten by the dog. 2.a lot of chocolates are eaten by us. 3.nice meals are cooked by the chef. 4. the books are bought by the pupils. 5. the letter is written by us. 6. they are offered new houses by me. 7. the mice are killed by the cat. 8. a good music is listened to by me. 9. a lot of books are read by mike. 10.my mother is loved by me. 11. celebrities are protected by the bodyguard. 12. my horse is ridden by my father every day. 13. football is played in most countries. 14. cricket isn't played in france. 15.he is well known by people. 16. babies are carried by mothers on their backs. 17. a house is built by him. 18. she is expected to come next week. 19. english is spoken by them in the office. 20. it is said the weather will be bad tomorrow. 21. the garages are cleaned by us every day. 22. the library is looked after by qualified librarians. 23. they are brought a message. 24. a present to his brother is given by my friend. 25. they are brought a message. 26. the car is repaired by the mechanic. 27. milk is used to make butter. 28. many countries are visited by him every year. 29. football is played by bob. 30. every day their room is swept by them. 31. the meal is always cooked by suzie. 32. we are taught latin by mr.ross.(latin is taught by mr.ross)

скорость волны = длина волны/ период колебаний

  v = λ/t = 270/ 13,5 = 20 м/с

t = 2l/c = (4,56*10^11)/3*10^8 = 1520 c 

ответ: 1520 с.