Giả sử \(\frac{a}{b}=\frac{c}{d}\Rightarrow\frac{a}{c}=\frac{b}{d}\)

\(\Rightarrow\left(\frac{a}{c}\right)^2=\left(\frac{b}{d}\right)^2=\frac{a^2+b^2}{c^2+d^2}\left(1\right)\)( áp dụng tính chất của dãy ts bằng nhau )

\(\Rightarrow\left(\frac{a}{c}\right)^2=\frac{a}{c}\cdot\frac{a}{c}=\frac{a}{c}\cdot\frac{b}{d}=\frac{ab}{cd}\left(2\right)\)

Từ (1)(2) => giả thiết thỏa mãn => đpcm

Cái này mik bt mik cần từ cái mũ 2 suy ra cái a/b=c/d cơ

Ban tự đo và vẽ hình nhá

a, Vì 2 tia oy, oz cx nằm trên 1 nửa mặt phẳng bờ chứa tia ox mà góc xoy= 30 độ< góc xoz = 120 độ nên tia oy nằm giữa 2 tia ox, oz

TC:

yoz+ xoy= xoz

Thay xoy=30 độ, xoz=120 độ, TC:

yoz+30 độ=120 độ

yoz=120 độ- 30 đô

yoz=90 đô

Vậy yoz = 90 dô

bạn có chắc chắn đúng hem

Góc AOC = 30^o => Góc DOB = 30^o ( đối đỉnh)

Góc AOD = 180 - 30 = 150 độ => góc BOC = 150 độ  ( đối đỉnh)

n là đường thẳng cắt nhau tại 1 điểm tạo thành 2n tia chunh gốc số góc tạo thành là 2n(2n-1)/2=n(2n-1)góc.không kể n góc bẹt 

thì số góc còn lại là n.(2n-1)-n=2n(n-1) mỗi góc trong số những góc này đều có một góc đối đỉnh với nó. vậy số cặp góc đối đỉnh với

nó là:2n(n-1)/2=n(n-1)

36.''Why are you looking at me that'' said the girl to the boy

The girl asked the boy why he was looking at her that

37. Mr Pike asked his daughter, ''How are you feeling now''

Mr Pike asked his daughter how she was feeling then

38. He said, '' I'm hungry now''

He said he was hungry then

39.''What do you want me to help you now'' she said to her son

She asked her son what he wanted her to help him then

40.''You have to explain all these things, son,'' said Miss Brown

Miss Brown told her son he had to explain all those things

41.The teacher said to the schoolgirl, ''What subject do you best''

The teacher asked the schoolgirl what subject she d best

42.The girl said to me, '' My brother and I will come to see you tomorrow evening''

The girl said to me her brother and she would come to see me tomorrow evening 

43.She said, ''I want to know how you can study new words quickly, Peter''

She said to Peter she wanted to know how he could study new words quickly

44.''Most of us have difficult in learning English,'' said the children

The children said most of them had difficult in learning English

45.My father said to me, ''What happened to your computer''

My father asked me what happened to my computer

46.''My father has just come back from my uncle's farm,'' said the boy

The boy said his father had just come back from his uncle's farm

47.''Why were you so late for the party lastnight'' he said to his friend

He asked his friend why he was so late for the party lastnight

48.The girl said, '' I must go home now because my parents have been waiting for me at home''

The girl said she had to go home then because her parents had  been waiting for her at home

49.''Shall we go to the English speaking club''

Andrew suggested going to the English speaking club

50.''Why don't we spend money on reseach into solar energy''

Anner suggested spending money on research into solar energy

51.''Why don't you sit down for a moment''

He suggested sitting down for a moment

52.''When will the course begin''

I asked her when the course would begin

53.''How much are the course fees''

I asked her how much the course fees were

54.''How long does the course take''

I asked her how long the course took

55.''How did you hear about the course''

She asked me how I had heard about the course

m.n giúp mk vs !!! bài này mai mk nộp r !!! Bài kiểm tra ấy ấy ấy !!!

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1.PHƯƠNG THỨC BIỂU ĐẠT : BIỂU CẢM+MIÊU TẢ

2 MK ĐẶT TÊN CHO BÀI THƠ LÀ: MẸ EM ĐI CẤY

Trong 31 số trên phải có ít nhất 1 số âm, không thì tổng 3 số bất kì đều là số dương trái với đề bài. Bỏ riêng 1 số âm vừa nói trên ra. Ta còn lại 30 số chia làm 10 cặp mỗi cặp 3 số. Tổng 3 số bất kì đều là âm nên cả 10 cặp tức 30 số còn lại đều là âm. Cộng với số âm bỏ riêng ta sẽ có tổng 31 số đều là số âm.