\(A=\cos^215^o-\cos^225^o+\cos^235^o-\cos^245^o+\cos^255^o-\cos^265^o+\cos^275^o\)

\(A=\sin^275^o-\sin^265^o+\sin^255^o-\sin^245^o+\cos^255^o-\cos^265^o+\cos^275^o\)

\(A=\left(\sin^275^o+\cos^275^o\right)-\left(\sin^265^o+\cos^265^o\right)+\left(\sin^255^o+\cos^255^o\right)-\sin^245^o\)

\(A=1-1+1-\frac{1}{2}\)

\(A=\frac{1}{2}\)

Áp dụng BĐT AM-GM ta có:

\(ab\le\frac{\left(a+b\right)^2}{4}\le\frac{1}{4}\)

Và \(P=a^2+b^2+\frac{1}{a^2}+\frac{1}{b^2}\)

\(=a^2+\frac{1}{16a^2}+b^2+\frac{1}{16b^2}+15\left(\frac{1}{16a^2}+\frac{1}{16b^2}\right)\)

\(\ge2\sqrt{a^2\cdot\frac{1}{16a^2}}+2\sqrt{b^2\cdot\frac{1}{16b^2}}+15\cdot2\sqrt{\frac{1}{16a^2}\cdot\frac{1}{16b^2}}\)

\(=\frac{1}{2}+\frac{1}{2}+15\cdot2\cdot\frac{1}{16ab}\)\(\ge1+15\cdot2\cdot\frac{1}{16\cdot\frac{1}{4}}=\frac{17}{2}\)

Xảy ra khi \(a=b=\frac{1}{2}\)

SƯU TẦM

50 Đề thi học sinh giỏi 

Anh Văn 9

Part 2:. Listen and write down the times in words. You will hear the recording three times. (9 points) 32

KỲ THI CHỌN HỌC SINH GIỎI LỚP 9 TOÀN HUYỆN 95

Năm học 2009-2010 95

MÔN: TIẾNG ANH 95

KỲ THI CHỌN HỌC SINH GIỎI LỚP 9 TOÀN HUYỆN 101

Năm học 2009-2010 101

MÔN: TIẾNG ANH 101

KỲ THI CHỌN HỌC SINH GIỎI LỚP 9 TOÀN HUYỆN 107

Năm học 2009-2010 107

MÔN: TIẾNG ANH 107

KỲ THI CHỌN HỌC SINH GIỎI LỚP 9 TOÀN HUYỆN 109

Năm học 2009-2010 109

MÔN: TIẾNG ANH 109

1. I'll ............................................................................................................................................... 138

II. READING 138

M«n tiÕng anh 142

M«n tiÕng anh 144

Question4: a) Change these sentences into passive voice 145

M«n tiÕng anh 146

Phßng Gi¸o Dôc §Ò thi chän häc sinh giái líp 9 THCS 147

Phßng Gi¸o Dôc §Ò thi chän häc sinh giái líp 9 THCS 149

Phßng Gi¸o Dôc §Ò thi chän ®éi tuyÓn häc sinh giái líp 9 THCS 150

N¨m häc 2004-2005 151

Question 8: Rewrite the following sentences, beginning each sentences with the cues 155

Question 8: Rewrite the following sentences, beginning each sentences with the cues 157

Question II:    Supply the corect form of the verbs in the brackets 158

than        B. with          C. at                   D. for 158

Question II:    Supply the corect form of the verbs in the brackets 160

M«n tiÕng anh 162

M«n tiÕng anh 164

M«n tiÕng anh 166

M«n tiÕng anh 168

Question 6: 172

a) Change these sentences into passive voice 172

Së Gi¸o dôc & §µo t¹o kú thi tuyÓn sinh vµo líp 10 – THPT chuyªn lam s¬n 173

Thanh ho¸     N¨m häc 2005-2006 173

Question4: a) Change these sentences into passive voice 175

Question II:    Supply the corect form of the verbs in the brackets. 181

Question II:    Supply the corect form of the verbs in the brackets. 182

Tr­êng thcs Nga Thuy 202

§Ò thi chän ®éi tuyÓn- §Ò 1 202

Häc sinh giái m«n tiÕng anh  lop 9- vong 2 202

N¨m häc 2008-2009- 120 phut 202

7.If anyone succeeds in solving the problems, it will probably be him. 202

VI  Use the following sets of words or phrases to write complete sentences . 204

VI  1. We haven't seen you for such a long time . 205

I. Choose the word in each group that has underlined part pronounced differently from the rest. Circile the letter you choose (5 p) 36

III. Choose the answer A,B,C or D to complete each sentence. Circle the letter you choose (10p) 36

12. The hotel room…over a very beautiful park 36

13. On Sundays in England, most shops were closed and…the theaters and cinemas 36

14. We didn’t…to the station in time to catch the train 36

15. Either John or his brothers…the money 36

16. I remember…the letter sometime ago but I can’t remember exactly when 36

17. Jane lost her case because it didn’t have…with hername on 36

18. Do you know what time the train…for Leeds? 36

19. The policeman warned us…there 36

20. The trip was very interesting. Jack wishes he…enough time to join 36

IV. Fill in the blank with the correct form of the words in capital letters (10 p) 36

V. Give the correct tense or form of the verbs in brackets to complete the following sentences (10p) 37

VI. Fill in each blank with one suitable preposition (10p) 37

VII. Fill in each numbered blank with one suitable word.(10p) 37

VIII. Read the passage carefully and choose the best answer A,B,C or D by circling the letter you choose (10 p) 37

X.Rewrite the sentences, beginning with the given words (10p) 38

Unless… 38

In case… 38

89.They are building a new museum in the city centre 38

X.Rewrite the sentences, beginning with the given words 

Mk đã in cho cậu đề thi hc sinh giỏi lớp 9  rồi nhưng mk ko thể copy cả nên cậu vào link này nhé !

http://s2.vndoc.com/data/file/2013/thang12/30/50-Bo-de-thi-HSG-Anhvan-9.doc

chỉ là đố vui thôi thay đổi ko khí

Ok !! chi tiết =))

\(\sqrt{6+\sqrt{24}+\sqrt{12}+\sqrt{8}}-\sqrt{4+2\sqrt{3}}\)

\(=\sqrt{1+2+3+2\sqrt{2}.\sqrt{1}+2\sqrt{2}.\sqrt{3}+2\sqrt{1}.\sqrt{3}}-\sqrt{3+2\sqrt{3}+1}\)

\(=\sqrt{\left(\sqrt{1}+\sqrt{2}+\sqrt{3}\right)^2}-\sqrt{\left(\sqrt{3}+1\right)^2}\)

\(=1+\sqrt{2}+\sqrt{3}-\sqrt{3}-1\)

\(=\sqrt{2}\)