ab;481 là sao

Á B C H K 1 2

Bài làm:

a) Ta có : \(\widehat{A_1}+\widehat{C}=90^o\)( 2 góc phụ nhau)

\(\widehat{A_2}+\widehat{B}=90^o\) ( 2 góc phụ nhau)

\(=>\widehat{A_1}+\widehat{C}+\widehat{A_2}+\widehat{B}=90^o+90^o\)

\(=>\left(\widehat{A_1}+\widehat{A_2}\right)+\left(\widehat{B}+\widehat{C}\right)=180^o\)

Mà \(\widehat{B}=2.\widehat{C}\) (gt)

\(=>90^o+2\widehat{C}+\widehat{C}=180^o\)

\(=>3\widehat{C}=90^o=>\widehat{C}=30^o\)

\(=>\widehat{B}=2.30^o=60^o\)

b) _ Xét tam giác AHC vuông tại H có:

\(\widehat{A_1}+\widehat{C}=90^o\) ( 2 góc phụ nhau)

\(=>\widehat{A_1}+30^o=90^o=>\widehat{A_1}=60^o\)

Hay \(\widehat{HAC}=60^o\)

c) _ Ta có : \(\widehat{B}+\widehat{BHK}=90^o\) ( 2 góc phụ nhau)

\(\widehat{A_1}+\widehat{C}=90^o\)( 2 góc phụ nhau)

Mà \(\widehat{B}=\widehat{A_1}\left(=60^o\right)\)

\(=>\widehat{BHK}=\widehat{C}\)

cậu có thể tham khảo bài làm trên đây ạ, chúc cậu học tốt :>

1.My dream is a luxury apartment house in the city center.

2.It is a high buildings surrounded by a swimming pool.

3.It is with 6 rooms very large and a balcony.

4.In my house,there are home robots to help me do the housework.

5.A super smart can help me watch programmes phone send and receive emails and contact my friends.

IV. Reading

 Read the following passage and decide whether the following information is True or False.

Human- robots Engineers are designing the next generation of robots which look, feel and act humans. It will be easier for people to work with them rather than cold machines. Realis looking hair and skin with sensors will allow robots to react naturally in the environment. For example, a robot can recognise and greet you when you touch its shoulder. Their eyes can move and blink. Their chests can move humans do when breathing. More specially, these robots can change their facial expressions so people might communicate naturally with them. These are needed for social robots of the future. It is believed that human- robots will appear everywhere and work as great assistants of humans in the robot era. Our future life might be more comfortable.

1. The generation of human- robots have been designed recently. T /_____F

2. People still cold machines more than this new generation of robots.T/___F

3. Robots of the new generation have hair, skin and eyes nearly humans.T/F____T

4. These robots don't know how to greet you when you touch their shoulder.T/F____F

5. Expressions on the faces of these robots are unchanged. T/F____F

Bài làm:

Ta có: \(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=\frac{1}{a+b+c}\)

\(\Leftrightarrow\frac{ab+bc+ca}{abc}=\frac{1}{a+b+c}\)

\(\Leftrightarrow\left(ab+bc+ca\right)\left(a+b+c\right)=abc\)

\(\Leftrightarrow a^2b+ab^2+c^2a+ca^2+b^2c+bc^2+2abc=0\)

\(\Leftrightarrow\left(a^2+2ab+b^2\right)c+ab\left(a+b\right)+c^2\left(a+b\right)=0\)

\(\Leftrightarrow\left(a+b\right)\left(ab+bc+ca+c^2\right)=0\)

\(\Leftrightarrow\left(a+b\right)\left(b+c\right)\left(c+a\right)=0\)

=> Hoặc a+b=0 hoặc b+c=0 hoặc c+a=0

=> Hoặc a=-b hoặc b=-c hoặc c=-a

Ko mất tổng quát, g/s a=-b

a) Ta có: vì a=-b thay vào ta được:

\(\frac{1}{a^3}+\frac{1}{b^3}+\frac{1}{c^3}=-\frac{1}{b^3}+\frac{1}{b^3}+\frac{1}{c^3}=\frac{1}{c^3}\)

\(\frac{1}{a^3+b^3+c^3}=\frac{1}{-b^3+b^3+c^3}=\frac{1}{c^3}\)

=> đpcm

b) Ta có: \(a+b+c=1\Leftrightarrow-b+b+c=1\Rightarrow c=1\)

=> \(P=-\frac{1}{b^{2021}}+\frac{1}{b^{2021}}+\frac{1}{c^{2021}}=\frac{1}{1^{2021}}=1\)

\(B=\frac{3^{10}.11+3^{10}.5}{3^9.2^4}=\frac{3^9.33+3^9.15}{3^9.2^4}\)

\(=\frac{3^9\left(33+15\right)}{3^9.2^4}=\frac{3^9.48}{3^9.16}\)

\(=\frac{48}{16}=3\)

\(B=\frac{3^{10}.11+3^{10}.5}{3^9.2^4}\)

    \(=\frac{3^{10}.\left(11+5\right)}{3^9.8}\)

    \(=\frac{3^{10}.16}{3^9.8}\)

     \(=\frac{3.2}{1}\)

    \(=6\)