Gọi G, I, H lần lượt là trọng tâm, tâm đường tròn ngoại tiếp và trực tâm của \(\Delta ABC\). Chứng minh \(\overrightarrow{IH}=3\overrightarrow{IG}\)

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BT7. Gọi (x;y) là tọa độ của D

a) ABCD là hbh khi và chỉ khi \(\overrightarrow{AB}=\overrightarrow{DC}\Rightarrow\left(-3;1\right)=\left(1-x;1-y\right)\Rightarrow\left\{{}\begin{matrix}1-x=-3\\1-y=1\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=4\\y=0\end{matrix}\right.\)

Vậy D(4;0) thỏa mãn yêu cầu bài toán

b) ABDC là hbh khi và chỉ khi 

\(\overrightarrow{AB}=\overrightarrow{CD}\Rightarrow\left(-3;1\right)=\left(x-1;y-1\right)\Rightarrow\left\{{}\begin{matrix}x-1=-3\\y-1=1\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=-2\\y=2\end{matrix}\right.\)

Vậy D(-2;2) thỏa yêu cầu bài toán

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ex2.

B - C - A - B - D - C - B - B - D - D - A - C - C - A - C - B - D - C - C - A

don't go

makes

cleans

would you be able

is

hears

will make

didn't belong

won

stops

will bury

would you do

knew

won't be

gave

doesn't start

won't let

goes

wouldn't have come

saw

wasn't - would buy

were - would accept 

study

was - would know

won't go

were - would live

will help

had

would invite

is

were

are kept

will have

ERROR IDENTIFICATION
Have you ever tried a strawberry pizza? If you went to Oxnard, the '' Strawberry Capital of California'' in May, you could!
Oxnard is in Southern California and this part of the state takes its strawberries very serious -> seriously.At the two-day California Strawberry Festival you can sample strawberries preparing -> prepared in all sorts of ways.In addition to traditional treatment -> treats such as strawberry shortcake, strawberry jam, strawberry tarts and strawberries dipped into chocolate, there is strawberry pizza! This dessert pizza is topped with strawberries, sour cream, cream cheese and whipped cream on a sweetened bread baked like a pizza.Strawberry kabobs dipped in powdered sugar are another delicacy.And drinks like a strawberry smoothie can wash it all down

I. Rewrite the sentences with the same meaning:
1. He plays badminton the best in my team.
=> No one in ……my team plays badminton better than him……..
2. This is the most difficult exercise in the book
=> No exercise in………the book is more difficult than this one………..
3. Do you have a more comfortable chair than this one?
=> Is this ………the most comfortable chair you have?………..
4. I have never seen a more boring film than this before.
=> This is the ………most boring film I've ever seen………..
5. She isn’t as beautiful as her mother.
=> He mother …………is more beautiful than her…………..
II.  Rearrange the words to make sentences.
6. ever/interesting/most/film/I/This/have/is/the/seen/that
=> ………This is the most interesting film that I have ever seen……………..
7. hotter and/ weather/The/getting/hotter/is
=> …………The weather is getting hotter and hotter…………..
8. father/ runner/faster/My/than/is/a/am/I.
=> …………My father is a faster runner than I am………..
III. Write NO MORE THAN THREE WORDS in each gap
9. Today is ………the longest…… day of the year (long) 
10. I have never tasted ……a more delicious………..cake than this one. (delicious)