\( [TEX]\frac{a}{c} = \frac{b}{d}[/TEX] \Rightarrow [TEX]ad=cb[/TEX] \Rightarrow [TEX]2ad=2cb[/TEX] \Rightarrow [TEX]ad-cb=cb-ad[/TEX] \Rightarrow[TEX]ab(ad-cb)=ab(cb-ad)[/TEX] \Rightarrow[TEX]a^2bd- acb^2= acb^2-a^2bd[/TEX] \Rightarrow[TEX]16a^2b^2-36abcd+24a^2bd-24acb^2 = 16a^2b^2- 36abcd+24acb^2-24a^2bd[/TEX] \Rightarrow[TEX]( 4a^2 - 6ac)(4b^2 + 6bd) =( 4a^2 +6ac)(4b^2 - 6bd)[/TEX] C2: [TEX]\frac{a}{c} = \frac{b}{d}[/TEX]\Rightarrow[TEX] (\frac{a}{b})^2=( \frac{c}{d})^2= \frac{ac}{bd}=\frac{-12ac}{-12bd}= \frac{(4a^2-6ac)-(4a^2+6ac)}{(4b^2- 6bd)- (4b^2+6bd)} [/TEX]\)
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2 after he had worked hard many years ,he retired
before he retired , he had worked hard many years
3 she bought this book two weeks ago
she has bought this book for 2 weeks
4 we last went to the cinema two weeks ago
we haven't gone to the cinema for 2 weeks
5 lt's over ten years since we got married
we have got married for 10 years
6 l have never read such an interesting novel befor
this is the first time I read such an interesting novel
7 we had luch and then went for a walk
after we had lunch , we went for a walk
8 how long have you learnt english ?
when did you learn E ?
9 the last time l saw jim was in 2004
l haven't seen Jim since 2004
10lt 's the coldest winter they've ever had
they have never had the coldest winter before
#Yumi
Tự vẽ hình
Ta có : \(CA . CE = CD . CB\)
\(\Rightarrow\) \(\dfrac{CA}{CD} = \dfrac{CB}{CE}\)
Xét \(\bigtriangleup{CAD} \) và \(\bigtriangleup{CBE}\) , có :
\(\widehat{BCE}\) : chung
\(\widehat{CDA} = \widehat{CBE} = 90 ^0\)
\(\Rightarrow\) \(\bigtriangleup{CAD}\) ~ \(\bigtriangleup{CBE}\) ( g.g)
\(\Rightarrow\) \(\dfrac{CA}{CB} = \dfrac{CD}{ CE}\)
\(\Rightarrow\) \(CA. CE = CB . CD\) (đpcm)
b, Xét \(\bigtriangleup{AQC}\) vuông tại Q , có : \(QE \perp AD\)
Áp dụng hệ thức \(b^2 = a . b'\) , có :
\(\Leftrightarrow\) \(CQ^2 = CA . CE \) (1)
Xét \(\bigtriangleup{CPB}\) vuông tại P , có : \(PD \perp BC\)
Áp dụng hệ thức \(b^2= a . b'\)
\(\Leftrightarrow\) \(CP^2 = CB . CD \) (2)
Vì \(CA . CE = CB . CD \) (cmt) (3)
Từ (1),(2) và (3) \(\Rightarrow\) \(CQ^2 = CP^2\)
\(\Rightarrow\) \(CQ = CP \) (đpcm)
I. Rewrite these sentences
1. Where are you from? ⇒⇒Where..DO YOU LIVE ?..
2. What is your job? ⇒⇒What .DO YOU DO ?....
3. She likes cooking? ⇒⇒She.IS INTERESTED IN COOKING...
4. Have you got a blck pen? ⇒⇒Do..YOU HAVE A BLACK PEN ?.
1. Learning English is very useful.
→→It's very useful to learn English.
2.They spent 2 years building this villa.
→→It took them 2 years to build this villa.
3.He didn't hurry,so he missed the train.
→→If he hadn't hurry, he wouldn't have missed the train.
4.Janet is te tallest student in her class.
→→No one is taller than Janet in her class.
5.The car was so expensive that i didn't bye it.
→→The car was too expensive for me to buy.
6.We started learning english more than 6 years ago
→→We have learnt E for more more than 6 years.
7.I last saw him 3 day ago.
→→I haven't seen him for 3 days.
8.The robbers made the bank manager hand over the money.
→→The bank manager was made to hand over the money.
9.We won't go on holiday because we don't have enough money
→→If we have enough money, we will go on holiday.
10.I think you should hand in your homework on time.
→→If i were you, I would hand in your homework on time.
11.If you don't water the plants regularly enough,they will die
→→Unless you water the plants regularly enough, they will die.
FIX
3.He didn't hurry,so he missed the train.
→→If....HE HADN'T HURRIED,HE WOULDN'T HAVE MISSED THE TRAIN..................................................
4.Janet is te tallest student in her class.
→→No one...IN HER CLASS IS TALLER THAN JANET..........................................
9.We won't go on holiday because we don't have enough money
→→If...WE HAD ENOUGH MONEY,WE WOULD GO ON HOLIDAY.....................................................
3Fenóng đỏ +2O2\(\rightarrow\)Fe3O4
Fe3O4+ 8HCl →FeCl2+2FeCl3 +4H2O
FeCl2 + 2NaOH →→Fe(OH)2+2NaCl
FeCl3 + 3NaOH →Fe(OH)3+3NaCl
4Fe(OH)2 + O2 +H2O → 4Fe(OH)3
2Fe(OH) \(\underrightarrow{to}\) Fe2O3+3H2O
1. Pleas don't make any noise; I'm very tired
⇒ I'd rather you didn't make any noise, I'm very tired.
Sắp xếp:
1. you/ mind/ if / I / stay / here?
⇒ Do you mind if I stay here ?
2. The concert hall / so crowded / I / see / hear / nothing.
⇒ The concert hall was so crowded that I saw and heard nothing.
3. It/ very kind / you / make friend / me.
⇒ It is very kind of you to make friend with me.