Oxit Bazo : Fe₂O₃ ; Cao ; Bao ;

Oxit Axit : SO₃ ; CO₂ ; N₂O₅

4P + 5O₂ ----> 2P₂O₅

2S + 3O₂ ----> 2SO₃

CaO + H₂O ----> Ca(OH)₂

mik nghĩ là BORING

----in Literature

Hello , my name is Duyen .Im grade 7 in a secondary school . I like many subject but my favourite subject is English . There are many reason i like it . First , if i speak English , i will have a good communication skills. Next , i can learn many new words and idioms . Moreover, i can easily understand the meaning if i listen to foreign songs .In addition, i can travel and have many foreign friends from all around the world . Lastly , in the future , if i study English , i can have a better job . In general . English is very interesting plus English lessons by the teacher at school made me love English . And i think you will too .

chúc bạn học tốt

tick mk ,mk tick lại cho

1 . what

2. where

3. who

4. what time

5.when

6.what

7.how many

8.how

9. what

10. how often

a. Ta có : ( a + b )( c - d ) = ac-ad+bc-bd (1)

( a - b )( c + d ) = ac+ad-bc+bd (2)

Từ giả thuyết : \(\dfrac{a}{b}=\dfrac{c}{d}\Rightarrow ad=bc\) (3)

Từ (1) , ( 2) và ( 3) \(\Rightarrow\)( a + b )( c - d) = ( a - b)( c + d )

\(\Rightarrow\dfrac{a+b}{a-b}=\dfrac{c+d}{c-d}\left(đpcm\right)\)

Ta có 3x=5y=7z suy ra \(\dfrac{x}{\dfrac{1}{3}}\)=\(\dfrac{y}{\dfrac{1}{5}}\)=\(\dfrac{z}{\dfrac{1}{7}}\)

Áp dụng tính chất dãy tỉ số bằng nhau , ta có:

\(\dfrac{x}{\dfrac{1}{3}}=\) \(\dfrac{y}{\dfrac{1}{5}}=\dfrac{z}{\dfrac{1}{7}}\)\(=\dfrac{x}{\dfrac{1}{3}}+\dfrac{y}{\dfrac{1}{5}}+\dfrac{z}{\dfrac{1}{7}}=\dfrac{x+y-z}{\dfrac{1}{3}+\dfrac{1}{5}-\dfrac{1}{7}}=\dfrac{41}{\dfrac{41}{105}}=105\)suy ra : x = 105 . \(\dfrac{1}{3}\)= 35

y = 105 . \(\dfrac{1}{5}\)= 21

z = 105 . \(\dfrac{1}{7}\)=15

Vậy : ...

100.0,8=80=>tự làm