Буду ( 30 ) составьте формулу выражающую к-й член последовательности, короче говоря найти ан(а энное): 1, 2, 6, 24,

Длина средней линии трапеции m равна полусумме длин оснований a и b: m = 0.5(a+b) допустим, а - большее основание, b - меньшее основание. тогда    по условию a : b = 7 : 3 отсюда a =  7b/3 длина средней линии дана: 40 = 0.5(a+b) подставляем вместо а выражение 7b/3: 40 = 0,5(7b/3 + b) 80 = (7b+3b)/3 80 = 10b/3 240 = 10b b = 24 см возвращаемся к а: a =  7b/3 = 7*24/3 = 7*3*8/3 = 56 а = 56 см проверка 40 = 0,5(24+56)  40 = 0,5*80 40=40 a: b =  56: 24 a: b = 7*8 : 3*8 a: b = 7: 3

We found ourselves short of water at hambledon lock; so we took our jar and went up to the lock-keeper’s house to beg for some.george was our spokesman. he put on a winning smile, and said: “oh, please could you spare us a little water? ”“certainly,” replied the old gentleman; “take as much as you want, and leave the rest.”“thank you so much,” murmured george, looking about him. “where – where do you keep it? ”“it’s always in the same place my boy,” was the stolid reply: “just behind you.”“i don’t see it,” said george, turning round.“why, bless us, where’s your eyes? ” was the man’s comment, as he twisted george round and pointed up and down the stream. “there’s enough of it to see, ain’t there? ”“oh! ” exclaimed george, grasping the idea; “but we can’t drink the river, you know! ”“no; but you can drink some of it,” replied the old fellow. “it’s what i’ve drunk for the last fifteen years.”george told him that his appearance, after the course, did not seem a sufficiently good advertisement for the brand; and that he would prefer it out of a pump.we got some from a cottage a little higher up. i daresay that was only river water, if we had known. but we did not know, so it was all right. what the eye does not see, the stomach does not get upset over.