Відрізок ak - бісектриса трикутника abc. знайдіть сторону bc,якщо ab: ac = 5: 3,bk-kc =4 см. , как можно быстрее!

Пусть ABCD -трапеция , AD || BC , BC< AD ; P(ABCD) =20 ,S((ABCD) =20 .
трапецию   можно вписать окружность;
MN ⊥ AD ; O ∈ [ MN ],  O -пересечения диагоналей(MN проходит через O).
M∈ [AD] ,N∈ [BC].

ON -?

S =(AB +BC) /2 *H ,где  H  - высота трапеции .
По условию задачи  трапеция описана  окружности , следовательно :
AD+BC =(AB +CD) = P/2 =20/2 =10.
AB =CD =5 ;
S =(AB +BC) /2 *H ;
20 =5*H ⇒ H =4.
Проведем BE ⊥AD и  CF ⊥ AD,
AE =DF =√(AB² -BE)² =√(AB² -H²)  =√(5² -4²) =3 .
AD -BC =2*3 =6.
{ AD -BC =6 ; AD +BC =10 ⇒AD =8 ; BC =2.
ΔAOD подобен ΔCOB :
BC/AD =ON/ OM ⇔BC/AD =ON/ (H -ON) .
2/8 =ON/ (4 -ON) ⇒ON =0,8.

ответ:  0,8.

1)I haven't eaten the cake yet

2. We used to love to eat meat

3. I was walking when it started to rain

4.he is as handsome as his dad

5.this dress is cheapest

6.we are as funny as our friends

7.she has never been to the forest

8. These nails are sharp as knives

9. I've never been to a recycling center before

10. They never rewrote d / z

11. have you already eaten?

12 Mom was reading a book when I asked for food

13. You just ate.

14. We have enough food.

15. This dress is too expensive to buy.

16. He's too smart not to learn.

17. I didn’t use old things again, but now I do.

18. We built a house

19. I was in New York in 1925

20.I think we will fly to Mars in the future. In the meantime, there is no need to know about it. ”

Объяснение:

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