ΔBDE vuông tại D

gọi F là trung điểm của BE​​

⇒​DF = \(\dfrac{1}{2}\) BE =BF

ΔBDF có BF = FD →​ Δ​BDF cân tại F

→\(\widehat{B}\)\(_1\) = \(\widehat{D}\)\(_2\)

lại có \(\widehat{B}\)\(_1\)= \(\widehat{B}\)\(_2\)

⇒\(\widehat{B}\)\(_2\) = \(\widehat{D}\)\(_2\)

mà 2 góc này ở vị trí so le trong ➜​ AB // DF

⇒​ \(\widehat{B}\) = ​\(\widehat{F}\)\(_1\) ( 2 góc đồng vị )

mặt khác ​​\(\widehat{B}\) = \(\widehat{C}\)\(_1\) ( Δ​ABC cân tại A )

⇒​​​​ \(\widehat{F}\) \(_1\) = \(\widehat{C}\)\(_1\) ⇒​ Δ​CDF cân tại D ⇒​ DF = DC

mà DF = \(\dfrac{1}{2}\) BE

⇒​ DC = \(\dfrac{1}{2}\) BE ⇒​​ BE = 2DC ( điều phải chứng minh )

đặt đa thức là f(x)

vì f(x) nhận 2/5 làm nghiệm ⇒ f(x) = ( x - 2/5 ) *g(x)

mặt khác f(x) nhận (-3) làm nghiệm ⇒ f(x) = ( x - 2/5 ) *( x + 3 ) *h(x)

với h(x) =1 ⇒ f(x) = ( x - 2/5 ) *( x + 3 ) = x\(^2\) + 13/5x - 6/5

a) đẳng nhiệt P\(_1\)V\(1\) = P​\(_2\)V​\(_2\)

⇒ P\(_1\)15 = P\(_2\) 45

⇒P\(_2\) = \(\dfrac{P_1}{3}\)

⇒ áp suất khối khí giảm 3 lần

b) thể tích không đổi \(\dfrac{P_1}{T_1}\) = \(\dfrac{P_2}{T_2}\)

⇒ ​\(\dfrac{T_1}{T_2}\) = \(\dfrac{P_1}{P_2}\) = \(\dfrac{100\%}{100\%+20\%}\) = \(\dfrac{5}{6}\)

⇒ \(\dfrac{T_1}{T_1+4}\) = \(\dfrac{5}{6}\)

⇒ T\(_1\) = 20

1. Thank you very much for a present which you sent me.

2. She was dancing with a student who had a slight limp

3. I am looking after some children who are terribly spoilt

4. The bed which I sleep on has no mattress.

5. Romeo and Juliet, whose parents hated each other, were lovers.

6. There wasn`t any directory in the telephone box which I was phoning from.

7. This is Mrs.Jones, whose son won the championship last year

8. I was sitting in a chair which suddenly collapsed

9. Mr.Smith, whom I had some specially to see, said he was too busy to speak to me.

10. The man whom I had some to see was sitting at the desk.

12. His girlfriend, who he trusted absolutely, turned out to be an enemy spy.

14. This is the story of a man whose wife suddenly loses her memory

15. We`ll have to get across the frontier, which will be difficult

16. a man brought in a small girl whose hand had been cut by flying glass

17. The car crashed into a queue of people, four of whom were killed

18. The roads were crowded with refugees, many of whom were wounded

19. The man who I was waiting for didn't turn up

20. Tom came to the party in patched jeans, which surprised the other guests, most of the other guests were wearing evening dress