a) x và y là hai đại lượng tỉ lệ nghịch theo hệ số a nên: 

`a=y/x=4/2=2`

b) Ta có: `a=2`

`=>y/x=2=>y=2x`

c) khi `y=-1=>2x=-1=>x=-1/2`

Khi `y=2=>2x=2=>x=1`

\(3x=2y\Rightarrow\dfrac{x}{2}=\dfrac{y}{3}\Rightarrow\dfrac{2x}{4}=\dfrac{3y}{9}\) \(\left(1\right)\)
\(y=2z\Rightarrow\dfrac{3y}{3}=2z\Rightarrow\dfrac{3y}{9}=\dfrac{2z}{3}\) \(\left(2\right)\)
Từ \(\left(1\right)\) và \(\left(2\right)\)
\(\Rightarrow\dfrac{2x}{4}=\dfrac{3y}{9}=\dfrac{2z}{3}\)
Áp dụng tính chất dãy tỉ số bằng nhau
ta có: \(\dfrac{2x}{4}=\dfrac{3y}{9}=\dfrac{2z}{3}=\dfrac{2x+3y-2z}{4+9-3}=\dfrac{40}{10}=4\)
+\(\dfrac{2x}{4}=4\Rightarrow2x=16\Rightarrow x=8\)
+\(\dfrac{3y}{9}=4\Rightarrow3y=36\Rightarrow y=12\)
+\(\dfrac{2z}{3}=4\Rightarrow2z=12\Rightarrow z=6\)
Vậy \(x=8;y=12;z=6\)

Cứu tui vs:((((

Điểm \(E\) ở đâu vậy bạn?

\(\dfrac{x+y}{x-y}=\dfrac{2}{5}\Rightarrow5\left(x+y\right)=2\left(x-y\right)\)

\(\Rightarrow5x+5y=2x-2y\)

\(\Rightarrow5x-2x=-2y-5y\)

\(\Rightarrow3x=-7y\)

\(\Rightarrow\dfrac{x}{y}=-\dfrac{7}{3}\)

giải thích nhiều cái nhỏ thành cái to

Những kẻ gian ác, bán nước như Ngô Đình Diệm đã " góp gió thành bão" thì đã phải nhận lấy sự chừng trị thích đáng mà chúng phải nhận

Lời giải:
a. Xét tam giác $BAD$ và $BHD$ có:

$\widehat{BAD}=\widehat{BHD}=90^0$

$BD$ chung

$\widehat{ABD}=\widehat{HBD}$ (do $BD$ là phân giác $\widehat{B}$)

$\Rightarrow \triangle BAD=\triangle BHD$ (ch-gn)

$\Rightarrow AB=BH$

b. Từ tam giác bằng nhau phần a suy ra $AD=DH$ (1)

Xét tam giác vuông $DHC$ vuông tại $H$ nên $DC> DH$ (do $DC$ là cạnh huyền) (2)

Từ $(1); (2)\Rightarrow DC> AD$

c.

Xét tam giác $BIH$ và $BCA$ có:

$\widehat{B}$ chung

$BH=BA$ (cmt)

$\widehat{BHI}=\widehat{BAC}=90^0$

$\Rightarrow \triangle BIH=\triangle BCA$ (g.c.g)

$\Rightarrow BI=BC$
$\Rightarrow BIC$ cân tại $I$

Hình vẽ:

2.MAI SPENT TWO HOURS CLEANING HER ROOM

3. WHO IS THE INVENTOR OF THIS MACHINE

4 HE IS THE YOUNGEST IN THE GROUP

5 I PREFER LISTENING TO MUSIC THAN WATCHING MOVIES

6 LET'S HAVE A DINNER AT MY HOUSE TONIGHT

7 MRS HOA CYCLES CAREFULLY AND SAFELY

tui lớp 6 nên ko chắc đâu đúng thì tick nhé

2. It took Mai two hours to clear out her room.                                                  (SPENT)

_____Mai spent two hours clearing out her room____________________________________________________________

3. Who invented this machine?                                                                         (INVENTOR)

_________Who was the inventor of this machine?________________________________________________________

5. No one in the group is younger than him.                                                      (YOUNGEST)

______He is the youngest one in the group___________________________________________________________

6. Listening to music is better than watching movies.                                          (PREFER)

_____I prefer listening to music to watching movies____________________________________________________________

7. What about having dinner at my house tonight?                                             (LET’s)

_____Let's have dinner at my house tonight____________________________________________________________

8. Mrs. Hoa is a careful and safe cyclist.                                                           (CYCLES)

_____Mrs Hoa cycles carefully and safely_______________________________________________________________

Bạn xem có đúng câu cuối không nhé

1 to => for

2 out => out of

3 coming => to come

4 putting => put

5 play => playing