Напишите, какое время в каждом предложении Past Simple, Present Perfect, Present perfect continuous.
1. Today is Thursday, and John has been late twice this week; he was late yesterday and on Monday.
2. I first met George a month ago, and I have met himseveral times since then.
3. It is October now, and we have done a lot of work this year; we did a lot last year too. 4. She bought a coat last winter, but she hasn't bought a new dress since 2008.
5. It's only the middle of the month, and he has already spent most of his salary; he spent $60 yesterday.
6.I broke my leg in 1991, but I have never broken my arm.
7. He's over sixty, and he's still working. He has been working hard all his life. When he was a young man, he sometimes worked all night.
8. The postman came at eight yesterday, but it's now half past eight and he hasn't come yet.
9. Today is May 25th. Ted hasn't been absent this month.
10. He felt extremely ill when he went to hospital, but he's felt much better since he came out of hospital a month ago.
Найдем ВС. По свойству медианы, проведенной к гипотенузе, ВС=2АМ=15*2=30 см.
ВМ=СМ=30:2=15 см.
Из прямоугольного треугольника АМН найдем МН.
МН=√(АМ²-МН²)=√(225-144)=√81=9 см.
НС=МС-МН=15-9=6 см.
Из треугольника АНС найдем АС:
АС=√(АН²+СН²)=√(144+36)=√180=6√5 см.
Найдем АВ:
АВ²=ВС²-АС²=900-180=720; АВ=√720=12√5 см.
sin A=sin 90°=1
sin B=AC\BC=6√5\30=√5\5
sin C=AB\BC=12√5\30=2√5\5
ответы: 30 см; 6√5 см; 12√5 см; 1; √5\5; 2√5\5.
Рассмотрим треугольник АВЕ:
Угол АЕВ=90 градусов, Гипотенуза АВ=32 см, Катет АЕ=16 см (по условию задачи)
По теореме Пифагора найдем второй катет (высоту):
ВЕ= √(АВ^2-АЕ^2)= √(32^2-16^2)= √(1024-256)= √768 см.
Теперь рассмотрим треугольник BДE:
ДЕ=АД-АЕ=40-16=24 см. ВЕ=√768 см. Угол ВЕД=90 градусов
По теореме Пифагора найдем ВД:
ВД=√(ВЕ^2+ВД^2)= √((√768)^2+24^2))= √(768+576)= √1344=8√21 см или приблизительно 36,66 см.
ответ: расстояние между вершинами тупых углов равно 8√21 см