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\(\frac{7}{15},\frac{8}{15},\frac{9}{15}\)nhé, e chỉ cần quy đồng 1/3 và 4/5 là tìm dc
thưa thánh BAC bằng 150 độ mà ABC bằng 60 độ vậy cái này là tam giác à
Vẽ hình phụ, tạo ra tam giác vuông đỉnh A để vận dụng hệ thức
\(\frac{1}{h^2}=\frac{1}{b^2}+\frac{1}{c^2}\)
Vẽ AH vuông BC; AF vuông AC (H,F thuộc BC)
Dễ thấy tam giác ABC đều:
\(\widehat{EAD}=\widehat{EAF}=45^o;\widehat{AED}=\widehat{AEF}=60^o\)
Tam giác AED=tam giác AEF (c.g.c). \(\Rightarrow AD=AF\)
Xét tam giác AFC vuông tại A.
\(\frac{1}{AC^2}+\frac{1}{AD^2}=\frac{1}{AH^2}\)
\(\Rightarrow\frac{1}{AC^2}+\frac{1}{AD^2}=\frac{4}{3}\) Vì \(AH^2=\frac{4}{3}\)
\(\RightarrowĐPCM\)
d, \(\left(-\frac{3}{4}+\frac{2}{5}\right):\frac{3}{7}+\left[\frac{3}{5}+\left(-\frac{1}{4}\right)\right]:\frac{3}{7}\)
\(=\frac{7}{20}:\frac{3}{7}+\frac{7}{20}:\frac{3}{7}\)
\(=0\)
3/5/7 là hỗn số nhé ba năm phần bảy
tương tự như mấy câu khác nhé
đề kiểm tra tiếng anh ne
I. Choose the word in each group that has the underlined part pronounced differently from the rest. (1 mark):
1. A. chair B. school C. couch D. children
2. A. sometimes B. moment C. stove D. close
3. A.biology B. geography C. physics D. fly
4. A. homework B. house C. hour D. here
II. Choose the best words by circling the letter A,B,C or D. (2 marks)
1. How ........ is it from your house to school?
A. far B. long C. old D. tall
2. What ......... intelligent boy!
A. the B. a C.an D. is
3. Would you some coffee?- __________
A. Yes, please B. Of course C. No, thanks D. Both A and C are correct.
4. This car is the ....... expensive of the four car.
A. Best B. more C. good D. most
5. They enjoy ........TV.
A. to watch B. watching C. to watching D. watched
6. A ..............work on a farm.
A. doctor B. farmer C. teacher D. journalist
7. She is very happy ........ you again.
A. meet B. meets C. to meet D. meeting
8. He is in class 7A and ............................... am I.
A. too B. so C. but D. by
III. Give the correct form of the verbs in the bracket. (2 marks)
1. Trang (not have) any friends in Ha noi. 1........................
2. Some boys and girls (play) marbles at the moment. 2........................
3. The students (visit) their old teacher next week? 3........................
4. Mr Nam usually (watch) TV in his free time? 4.......................
IV. Fill in the blanks with the correct form of the words in the capital letters (1 mark):
1. Today Lien is not....................because she misses her parents HAPPINESS
2. Living in the city is..................than living in the countryside NOISY
3. In electronics, we learn to repair. .........................appliances. HOUSE
4. My. ......................is tall and beautiful. TEACH
V. Read the passage carefully then answer the questions: (2 marks)
Linda lives with her parents in a big house in HCM City. She is from England. She is thirteen. She has blue eyes and black hair. She is studying at International Language School. She can speak French, English and Vietnamese. But she doesn't speak Vietnamese fluently. She often goes to French speaking club on Sunday mornings. She s Vietnamese people very much because they are friendly.
1. Where is Linda from?.........................................................................................
2. How many languages can she speak?........................................................................
3. Does she speak Vietnamese fluently?.......................................................................
4. Why does she Vietnamese people?..................................................................
VI. Arrange the following words to make correct sentences. (1 mark).
1. play/ will/ soccer/ this/ afternoon/ they.
.............................................................................................
2. my/ is/ favorite/ English/ subject.
.............................................................................................
VII. Complete the following sentences with the suggested words. (1 mark).
1. It / difficult/ find/ apartment / Ho Chi Mih City?
..................................................................................................
2. They/ listen/ music/ now.
Đặt \(A=\frac{3-4X}{X^2+1}\)
Ta có: \(A=\frac{X^2-4X+4-\left(X^2+1\right)}{X^2+1}=\frac{\left(X-2\right)^2}{X^2+1}-1\ge-1\)
(Vì \(\frac{\left(X-2\right)^2}{X^2+1}\ge0\))
\(\Rightarrow MinA=-1khiX=2\)
Ta có:\(A=\frac{4\left(X^2+1\right)-\left(4X^2+4+1\right)}{X^2+1}=4-\frac{\left(2X+1\right)^2}{X^2+1}\le4\)
(Vì \(-\frac{\left(2X+1\right)^2}{X^2+1}\le0\))
\(\Rightarrow MaxA=4khiX=-\frac{1}{2}\)
Học tốt
viết lại đề tí :
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2017.2018}\)
= \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{2017}-\frac{1}{2018}\)
= 1 - \(\frac{1}{2018}\)
= \(\frac{2017}{2018}\)
Ta có:
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2017.2018}\)
\(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2017}-\frac{1}{2018}\)
\(=\frac{1}{1}-\frac{1}{2018}\)
\(=\frac{2017}{2018}\)