1. Mr . Hien isn't \(\Rightarrow\) doesn't live in a house in the country.

(tobe không đi cùng động từ nha)

2. The Browns are traveling to HCM City in \(\Rightarrow\) by train.

(by + phương tiện)

3.There aren't a \(\Rightarrow\) any trees to the left of Lan's house

(phủ định dùng any)

4.That's my sister over there . She stands\(\Rightarrow\)is standing near the window . (câu này là thì hiện tại tiếp diễn nha)

5.Do you know how many teachers does our school have \(\Rightarrow\) our school has ?

(vì có Do you know nha)

Balanced diet means you eat a variety of foods without eating too much of anything

hình tự vẽ nha !

Chứng minh

a, Xét \(\Delta ABD\) và \(\Delta ACE\) có :

AB = AC (gt)

\(\widehat{ABD}=\widehat{ACE}\) (bù với hai góc bằng nhau)

BD = CE (gt)

\(\Rightarrow\Delta ABD=\Delta ACE\left(c.g.c\right)\)

\(\Rightarrow AD=AE\) (hai góc tương ứng)

\(\Rightarrow\Delta ADE\) cân

b, Ta có : AD = DB (= BC)

\(\Rightarrow\Delta ABD\) cân (1)

Lại có : \(\widehat{ABD}+\widehat{ABC}=180^O\)

\(\Rightarrow\widehat{ABD}=180^O-\widehat{ABC}\)

\(\widehat{ABD}=180^O-60^O=120^O\)

Từ (1) \(\Rightarrow\widehat{DAB}=\dfrac{180^O-\widehat{ABD}}{2}=\dfrac{180^O-120^O}{2}=30^O\)

mà \(\widehat{DAB}=\widehat{CAE}\) (\(\Delta ABD=\Delta ACE\) )

\(\Rightarrow\widehat{DAE}=\widehat{DAB}+\widehat{BAC}+\widehat{CAE}=30^O+60^O+30^O=120^O\)

góc B là 54 độ

\(C=\dfrac{1}{100}-\dfrac{1}{100.99}-\dfrac{1}{99.98}-\dfrac{1}{98.97}-...\dfrac{1}{3.2}-\dfrac{1}{2.1}\)

\(=-\left(\dfrac{1}{100.99}+\dfrac{1}{99.98}+\dfrac{1}{98.97}+...+\dfrac{1}{3.2}+\dfrac{1}{2.1}\right)+\dfrac{1}{100}\)

\(=-\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{97.98}+\dfrac{1}{98.99}+\dfrac{1}{99.100}\right)+\dfrac{1}{100}\)

\(=-\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{97}-\dfrac{1}{98}+\dfrac{1}{98}-\dfrac{1}{99}+\dfrac{1}{99}-\dfrac{1}{100}\right)+\dfrac{1}{100}\)

\(=-\left(1-\dfrac{1}{100}\right)+\dfrac{1}{100}\)

\(=\left(-1\right)+\dfrac{1}{50}=-\dfrac{49}{50}\)