Основания bc и ad трапеции abcd равны соответствено 5см и 20см, диагональ bd=10см.докажите, что треугольники cbd и bda подобные

Bd/ad=bc/bd. 10/20=5/10 треугольники cbd и bda подобны

проверим на подобие: вд/ад= вс/вд. 10/20= 5/10. выполняется. значит, подобны.

По условию четыре данные прямые параллельны, отсекают на прямой ЕН отрезки, равные длине отрезка ЕF, т.е. 6 см.

Значит, ЕН=3•6=18 см

CD=CB=AB=4, и AD=3•4=12 см

Проведем параллельно AD прямую ЕМ, пересекающую параллельные прямые СF и BG в точках Т и К соответственно.

СТ=ВК=АМ=DE=51 см.

ТF=CF-51=57-51=6 см,

Соответственные углы при пересечении параллельных прямых секущими равны (свойство), ⇒

∆ ТЕF, ∆ KEG и ∆ МЕН подобны;

TF - средняя линия ∆ КЕG ⇒ KG=2•TF=12 см

BG=51+12=63 см

КT=КМ=ТЕ=4

У подобных ∆ ТЕF и ∆ МEН k=EH:EF=18:6=3⇒

MH=6•3=18 см

Итак, АD=3•4=12 см,

EH=18 см

DE=51; CF=57 см

AH=51+18=69 см

Нужно металлических прутьев

12+18+57+63+69+51=30+120+120=270 cм =2,7 м

ответ:2,7 м.

Agriculture and manufacturing important in all industries.

a)is b) are c) have d) be

2)Consumers .. for some services.

a)does not pay b) does not pays c) do not pay d) not pay

3) What is right for 3 298?

- two thousands two hundred and ninety eight

-two thousand two hundred and ninety eight

4)It is .. to develop agriculture.

a)essential b) nice c) impossible

5) Producers study the market situation (чтобы знать) how many goods to produce. a)to know b) that to know c) to knowing

6)We … … economics last year.

a) didn’t studied b) weren’t studied c) didn’t study d) not studied

7)New workers ……… by the company every year.

a)are employed b) are employing c) employed d) do employ

8)What is right for 2004?

-twenty and four

-twenty oh four

-two thousand and four

9) Living conditions in this country are .. than in my country.

a)badder b) more bad c) worst d) worse

10) The supply of fuel is the .. problem for many European countries.

a)most serious b) more serious c) least serious d) serious

11) I have lived in this country ... 5 years.

a) for b) since c) more d) -

12)They dont have competitors on this market.

a)some b) ever c) any d) a

13) I havent seen him .. he graduated from university.

a)from time b) since c) yet d) for

14)Put the words into the right order: productivity increased recently company has The its.

15)Where . . . his articles last year?

a)did the scientist publish b) does the scientist publish c) has the scientist published