$\begin{array}{l}\tan \left( {{{90}^o} - \alpha } \right) = \cot \alpha ,{\sin ^2}\alpha = {\cos ^2}\left( {{{90}^o} - \alpha } \right)\\ \Rightarrow \tan {30^o} = \cot {60^o}\\A = \tan {30^o}.{\sin ^2}{39^o} + \cot {60^o}{\sin ^2}{51^o}\\A = \tan {30^o}\left( {{{\sin }^2}{{39}^o} + {{\sin }^2}{{51}^o}} \right)\\A = \tan {30^o}\left( {{{\sin }^2}{{39}^o} + {{\cos }^2}{{39}^o}} \right) = \tan {30^o}\\ = \dfrac{{\sqrt 3 }}{3}\end{array}$
$\text{Ta có các công thức }$
$\text{α+β=90⇒cot(α)=tan(β);cos(α)=sin(β)}$
$\text{Sin²α+Cos²α=1}$
$\text{A=tan30⁰.sin²39⁰+cot60⁰.sin²51⁰}$
$\text{ =tan30⁰sin²39⁰+tan30⁰.cos²39⁰}$
$\text{=tan30⁰.(sin²39⁰+cos²39⁰)}$
$\text{=tan30⁰}$
$\text{= $\frac{1}{\sqrt[]{3}}$}$
Đố ai vẽ đc anime đam mỹ Ai vẽ đc+nhanh mk cho hay nhất nhé
bài 17 ạ, đừng làm tắt ạ , e cảm ơn
Bài 4:Tìmx ,biết: a. (x – 30) – 40 = 0 b. 200+ (118 – x) = 307 c. 176 – (x + 21) = 80 Bài 5:Tính: a) 1- 2 + 3 - 4 + 5 - 6 + 7 - 8 + 9. b) 1 - 3 + 5 - 7 + 9 - 11 + … + 91 - 93 + 95 - 97 + 99. Bài 6 :Lớp 6A có 33họcsinh, lớp 6B có 32 họcsinh, lớp 6C có 27 họcsinh . Hỏicảbalớp 6A; 6B; 6C cóbaonhiêuhọcsinh ? Bài 7:Mộttrường THCS cósốhọcsinhcủakhốilớp 6 là 102 HS, khốilớp 7 cónhiềuhơnkhốilớp 6 là13 HS, khốilớp 8 cóíthơnkhốilớp7 là 9 HS, khốilớp 9 cóíthơnkhối 8 là 5 HS. Tínhsốhọcsinhtoàntrườngcủatrường THCS đó? Giúp mik nha
Đề bài : Changes the sentences into passive voice
Cho 2 nguồn sáng A và B . Hãy có các vùng tối xuất hiện trên màn chắn
Cho A nằm ngoài đường tròn tâm O. Vẽ tiếp tuyến ADC không qua O (D nằm giữa A và C). Chứng minh (AD/AC)=(BD^2/BC^2)
giúp em với mấy anh cj ơi mai em nộp rùi :<<
Làm ơn hãy giải dùm em, nếu được xin hãy giải thích từng câu. Xin Cảm Ơn Make one sentence from each group of sentences, beginning as shown. a) I got on a train. I wanted to go to a station. The train didn't stop there. The train I …………………………………………………... b) I read a book. You recommended a book to me. This was the book. The book I ....................................................................................... c) The ship hit an iceberg and sank. Warning messages had been sent to it. The ship ignored these. The ship, ............................................................................ d) The postman realised I was on holiday. You had sent me a parcel. The postman left it next door. The postman, ............................................................................................... e) I used to own a dog. People came to the door. The dog never barked at them. The dog I ................................................................................................... f) I bought my car from a woman. She lives in a house. You can see the house over there. The woman I ................................................................................ g) We went to a beach on the first day of our holiday. It was covered in seaweed. This smelled a lot. The beach we ..................................................................................................... h) My neighbours have three small children. The children make a lot of noise. My neighbours never apologise. My neighbours, ............................................................................................... i) I bought a new computer. It cost me a lot of money . The new .............................................................................................................
III. Đổi các câu sau sử dụng với Because of: 1.Mary did not go to school because she was sick. …………………………………………………………………………………………….…… 2. I can not eat these fruits because they are green. ………………………………………………………………………………………………..… 3. We could not do the test well since it was really difficult. ………………………………………………………………………………………………….. 4. The train come late because it was foggy. ………………………………………………………………………………………………….. 5. I can not sleep as the weather is quite hot . ………………………………………………………………………………………………...... 6. He could not drive fast because the street was crowded and narrow. ………………………………………………………………………………………………….. 7. All the shops will be closed because tomorrow is a public day. ………………………………………………………………………………………………….. 8. They will leave early because the distance is very long. ………………………………………………………………………………………………….. 9. She loves him because he is kind. ………………………………………………………………………………………………….. 10. Hang went to bad early because she felt tired .................................................................................................................
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