a. vì HT ABCD có AD//BC => A+B=180(2 góc kề 1 cạnh bù nhau)

b. vì HT ABCD có AD//BC => C+D=180 

    Vậy A+B=C+D(=180)

c. ta có: A+B=180 , A-B=20

   => 2A=200 ->A=100, B=100-20=80

   ta có: C+D=180 , D=2C

       => C+2C=180

              3C=180

               C=60 -> D=2.60=120

Vậy A=100,B=80,C=60,D=120

( 3 ¹⁰¹ - 3 ) : 2

4^2 . 120 - 64 . 17 + 16 . 34

=16 . 120 - 64 . 17 + 16 . 34

=16.(120+34)-64.17

=16.154-64.17

=2464-1088

=1376

- Trọng lực đã tác động lên quả bóng, quả táo, hạt mưa làm chúng rơi xuống.

- Lực làm quả bóng, quả táo rơi xuống có phương thẳng đứng và có chiều hướng về phía Trái Đất.

chưa hk

\(\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{-1}{90}\)

\(=\dfrac{-1}{4.5}+\dfrac{-1}{5.6}+\dfrac{-1}{6.7}+\dfrac{-1}{7.8}+\dfrac{-1}{8.9}+\dfrac{-1}{9.10}\)

\(=\dfrac{-1}{4}-\dfrac{-1}{5}+\dfrac{-1}{5}-\dfrac{-1}{6}+\dfrac{-1}{6}-\dfrac{-1}{7}+\dfrac{-1}{7}-\dfrac{-1}{8}+\dfrac{-1}{8}-\dfrac{-1}{9}+\dfrac{-1}{9}-\dfrac{-1}{10}\)

\(=\dfrac{-1}{4}-\dfrac{-1}{10}\)

\(=\dfrac{-3}{20}\)

1. The doctor says that if my father continues to smoke he 'll be ill

\(\Rightarrow\) The doctor says unless my father stops smoke, he'll be ill

2. Does astronomy interest you?

\(\Rightarrow\) Do you take an interest in astronomy?

1 .The new pool is near to my house

\(\Rightarrow\) It's not far from my house to the new pool

2 .If you cannot swim, you are not allowed in the deep end

\(\Rightarrow\) You are not allowed in the deep end unless/except if/until/till/before you can swim.

3 . Football is the most popular sport at the centre.

\(\Rightarrow\) Football is more popular than any other sport at the sports centre.

4 .No members cannot enter the sports centre

\(\Rightarrow\) Non-members aren't allowed to enter the sports centre without a ticket.

5. I didn't go swimming with Sam because I was very busy

\(\Rightarrow\) I was too busy to go swimming with Sam

6. They started to learn English 3 years ago

\(\Rightarrow\) They have been learning English for three years.