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W-ai? Li-ve a co-ment

đề khó hiểu quá

Chỉ cần hỏi một câu thôi là biết có chỗ trống để ngồi hay không?

Xin lỗi, mọi người làm ơn cho hỏi có còn chỗ trống để ngồi đợi xe bus không a?

Before:

Build an emergency kit and make a family communications plan.

Avoid building in a floodplain unless you elevate and reinforce your home.

Elevate the furnace, water heater and electric panel in your home if you live in an area that has a high flood risk.

Consider installing "check valves" to prevent flood water from backing up into the drains of your home.

If feasible, construct barriers to stop floodwater from entering the building and seal walls in basements with waterproofing compounds.

During:

Listen to the radio or television for information.

Be aware that flash flooding can occur. If there is any possibility of a flash flood, move immediately to higher ground. Do not wait for instructions to move.

Be aware of stream, drainage channels, canyons and other areas known to flood suddenly. Flash floods can occur in these areas with or without typical warnings such as rain clouds or heavy rain.

After:

Avoid moving water.

Stay away from damaged areas unless your assistance has been specifically requested by police, fire, or relief organization.

Emergency workers will be assisting people in flooded areas. You can help them by staying off the roads and out of the way.

Play it safe. Additional flooding or flash floods can occur. Listen for local warnings and information. If your car stalls in rapidly rising waters, get out immediately and climb to higher ground.

Return home only when authorities indicate it is safe.

Before:

• Build an emergency kit and make a family communications plan.
• Avoid building in a floodplain unless you elevate and reinforce your home.
• Elevate the furnace, water heater and electric panel in your home if you live in an area that has a high flood risk.
• Consider installing "check valves" to prevent flood water from backing up into the drains of your home.
• If feasible, construct barriers to stop floodwater from entering the building and seal walls in basements with waterproofing compounds.

During:

• Listen to the radio or television for information.
• Be aware that flash flooding can occur. If there is any possibility of a flash flood, move immediately to higher ground. Do not wait for instructions to move.
• Be aware of stream, drainage channels, canyons and other areas known to flood suddenly. Flash floods can occur in these areas with or without typical warnings such as rain clouds or heavy rain.

After:

• Avoid moving water.
• Stay away from damaged areas unless your assistance has been specifically requested by police, fire, or relief organization.
• Emergency workers will be assisting people in flooded areas. You can help them by staying off the roads and out of the way.
• Play it safe. Additional flooding or flash floods can occur. Listen for local warnings and information. If your car stalls in rapidly rising waters, get out immediately and climb to higher ground.
• Return home only when authorities indicate it is safe.

a: ΔABC vuông tại A

mà AM là đường trung tuyến

nên MA=MB=MC

Xét tứ giác AMCD có

AM//CD

CM//AD

Do đó: AMCD là hình bình hành

Hình bình hành AMCD có MA=MC

nên AMCD là hình thoi

b: Xét ΔAHI vuông tại H và ΔBAC vuông tại A có

\(\hat{HAI}=\hat{ABC}\) (hai góc đồng vị, AH//BC)

Do đó: ΔAHI~ΔBAC

a) Ta có: E,F lần lược là hình chiếu của B,C trên AD 

\(\Rightarrow\left\{{}\begin{matrix}\widehat{BEA}=90^o\\\widehat{CFA}=90^o\end{matrix}\right.\) 

Xét hai tam giác ABE và ACF có:

\(\widehat{BEA}=\widehat{CFA}\left(=90^o\right)\) 

\(\widehat{BAE}=\widehat{CAF}\) (do AD là phân giác của góc A) 

\(\Rightarrow\Delta ABE\sim\Delta ACF\left(g.g\right)\)  

b) Xét hai tam giác BDE và CDF có:

\(\widehat{BDE}=\widehat{CDF}\) (đối đỉnh) 

\(\widehat{BED}=\widehat{CFD}\left(=90^o\right)\)

\(\Rightarrow\Delta BDE\sim\Delta CDF\left(g.g\right)\) 

\(\Rightarrow\dfrac{BE}{CF}=\dfrac{DE}{DF}\) (1) 

Mà: \(\Delta ABE\sim\Delta ACF\left(cmt\right)\)

\(\Rightarrow\dfrac{BE}{CF}=\dfrac{AE}{AF}\left(2\right)\)

Từ (1) và (2) ta có: \(\dfrac{DE}{DF}=\dfrac{AE}{AF}\Rightarrow AF\cdot DE=AE\cdot DF\) 

a) Xét hai tam giác ABE và ACD có:

\(\widehat{ACD}=\widehat{ABE}\left(gt\right)\)     

\(\widehat{BAC}\) chung 

\(\Rightarrow\Delta ABE\sim\Delta ACD\left(g.g\right)\) 

b) Ta có: \(\Delta ABE\sim\Delta ACD\left(cmt\right)\)

\(\Rightarrow\dfrac{AB}{AC}=\dfrac{AE}{AD}\) 

a) Ta có:

M là trung điểm của AB

N là trung điểm của AC 

⇒ MN là đường trung bình của tam giác ABC  

⇒ MN // BC 

\(\Rightarrow\widehat{AMN}=\widehat{ABC}\) (đồng vị) 

Xét hai tam giác ABC và AMN có:

\(\widehat{AMN}=\widehat{ABC}\left(cmt\right)\)

\(\widehat{BAC}\) chung 

\(\Rightarrow\Delta ABC\sim\Delta AMN\left(g.g\right)\) 

b) Chứng minh tương tự như câu a thì ta có: 

PN cũng là đường trung bình của tam giác ABC \(\Rightarrow PN=\dfrac{1}{2}AB\)

PM cũng là đường trung bình của tam giác ABC \(\Rightarrow PM=\dfrac{1}{2}AC\)

Mà: \(NM=\dfrac{1}{2}BC\) (NM là đường trung bình ...) 

Xét hai tam giác ABC và PNM có:

\(\dfrac{PN}{AB}=\dfrac{PM}{AC}=\dfrac{NM}{BC}=\dfrac{1}{2}\)  

\(\Rightarrow\Delta ABC\sim\Delta PNM\left(c.c.c\right)\)

a) Áp dụng định lý Py-ta-go cho tam giác ABC vuông tại A ta có:

\(BC^2=AB^2+AC^2\) 

\(\Rightarrow BC=\sqrt{AB^2+AC^2}\)

\(\Rightarrow BC=\sqrt{10^2+20^2}=10\sqrt{5}\left(cm\right)\) 

Áp dụng định lý Py-ta-go cho tam giác ABM vuông tại A ta có:

\(BM^2=AB^2+AM^2\)

\(\Rightarrow BM=\sqrt{AB^2+AM^2}\)

\(\Rightarrow BM=\sqrt{10^2+5^2}=5\sqrt{5}\left(cm\right)\)

b) Ta có: 

\(\dfrac{AM}{AB}=\dfrac{1}{2}\)

\(\dfrac{BM}{BC}=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{AM}{AB}=\dfrac{MB}{BC}=\dfrac{1}{2}\) 

Xét hai tam giác ABC và AMB có: 

\(\widehat{BAC}\) chung 

\(\dfrac{AM}{AB}=\dfrac{MB}{BC}=\dfrac{1}{2}\)

\(\Rightarrow\Delta ABC\sim\Delta AMB\left(c.g.c\right)\)

Áp dụng định lý Py-ta-go cho tam giác ABC vuông tại A ta có:

\(BC^2=AB^2+AC^2\)

\(\Rightarrow BC=\sqrt{AB^2+AC^2}\)

\(\Rightarrow BC=\sqrt{3^2+4^2}=5\left(cm\right)\)

Ta có:

\(\dfrac{AB}{DE}=\dfrac{3}{15}=\dfrac{1}{5}\)

\(\dfrac{AC}{DF}=\dfrac{4}{20}=\dfrac{1}{5}\)

\(\dfrac{BC}{EF}=\dfrac{5}{25}=\dfrac{1}{5}\)  

\(\Rightarrow\dfrac{AB}{DE}=\dfrac{AC}{DF}=\dfrac{BC}{EF}=\dfrac{1}{5}\)
Xét hai tam giác ABC và DEF có:

\(\dfrac{AB}{DE}=\dfrac{AC}{DF}=\dfrac{BC}{EF}\left(=\dfrac{1}{5}\right)\)

\(\Rightarrow\Delta ABC\sim\Delta DEF\left(c.c.c\right)\)