a+b=...+a
(a+b)+c=a(...+c)
a+o=o+...=...
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a)
Xét \(\Delta AOD\) và \(\Delta COB\) có: \(\left\{{}\begin{matrix}OA=OC\left(gt\right)\\\widehat{O}:chung\\OB=OD\left(gt\right)\end{matrix}\right.\)
\(\Rightarrow\Delta AOD=\Delta COB\left(c.g.c\right)\)
\(\Rightarrow AD=BC\left(\text{2 cạnh tương ứng}\right)\left(\text{đpcm}\right)\)
b)
Nối A với C
Ta có: \(\left\{{}\begin{matrix}OA=OC\\OB=OD\end{matrix}\right.\left(gt\right)\Rightarrow OA-OB=OC-OD\)
Hay \(AB=CD\)
Xét \(\Delta ABC\) và \(\Delta CDA\) có: \(\left\{{}\begin{matrix}AB=CD\left(cmt\right)\\AC:chung\\AD=BC\left(cmt\right)\end{matrix}\right.\)
\(\Rightarrow\Delta ABC=\Delta DCA\left(c.c.c\right)\)
\(\Rightarrow\widehat{ABC}=\widehat{CDA}\left(\text{2 góc tương ứng}\right)\)
Vì \(\Delta AOD=\Delta COB\left(cmt\right)\Rightarrow\widehat{A}=\widehat{C}\left(\text{2 góc tương ứng}\right)\)
Xét \(\Delta ABE\) và \(\Delta CDE\) có: \(\left\{{}\begin{matrix}\widehat{ABC}=\widehat{CDA}\left(cmt\right)\\AB=CD\left(cmt\right)\\\widehat{A}=\widehat{C}\left(cmt\right)\end{matrix}\right.\)
\(\Rightarrow\Delta ABE=\Delta CDE\left(g.c.g\right)\left(\text{đpcm}\right)\)
c) Vì \(\Delta ABE=\Delta CDE\left(cmt\right)\Rightarrow AE=CE\left(\text{2 cạnh tương ứng}\right)\)
Xét \(\Delta AOE\) và \(\Delta COE\) có: \(\left\{{}\begin{matrix}OA=OC\left(gt\right)\\\widehat{A}=\widehat{C}\left(cmt\right)\\AE=CE\left(cmt\right)\end{matrix}\right.\)
\(\Rightarrow\Delta AOE=\Delta COE\left(c.g.c\right)\\ \Rightarrow\widehat{AOE}=\widehat{COE}\left(\text{2 góc tương ứng}\right)\)
`=> OE` là phân giác của \(\widehat{xOy}\) (đpcm)
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I.Find the word which has a different sound in the part underlined.
1. A.coffee B.pot C.bottle D.one
2. A.hat B.map C.what D.cap
3. A.what B.yogurt C.problem D.morning
4. A.was B.wall C.walk D.water
5. A.talk B.salt C.sausage D.cause
6. A.flower B.flour C.cow D.pork
7. A.soon B.food C.noodle D.cook
8. A.wash B.warm C.wall D.walk
9. A.morning B.forty C.forget D.pork
10. A.wash B.bag C.pan D.add
11. A.aunt B.sauce C.caught D.daughter
12. A.daughter B.sauce C.laundry D.aunt
13. A.wash B.draw C.on D.off
14. A.bottle B.roll C.soft D.coffee
15. A.document B.naughty C.water D.audience
1.D
2.C
3.D
4.A
5.C
6.D
7.D
8.A
9.C
10.A
11.A
12.D
13.A
14.B
15.A
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1. A. local B. flower C. poster D. host
2. A. April B. plant C. candle D. many
3. A. single B. sign C. younger D. angry
4. A. exhaust B. harm C. hole D. hide
5. A. cow B. now C. know D. town
Ex 2 : Odd one out
1. A. lovely B. beautiful C. slowly D. careless
Ex 1 :
1. A. local B. flower C. poster D. host
2. A. April B. plant C. candle D. many
3. A. single B. sign C. younger D. angry
4. A. exhaust B. harm C. hole D. hide
5. A. cow B. now C. know D. town
Ex 2 : Odd one out
1. A. lovely B. beautiful C. slowly D. careless
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Câu 1
a black b hand c orange d matter
Câu 2
a coffee b cold c ocean d kilo
Câu 3
a summer b uncle c population d minibus
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