Trên này ít người học c3 lắm :<

q1.q2>0 nhé bạn 2 cái đẩy nhau => cùng dấu

Dear Liu!

Last time I told you that I had been thinking about pursuing higher education in the UK. I got started to learn the process of applying for a university in London some time ago. Now I have some questions for you. 

First, what is the procedure for applying for a student visa? Of course. I have to submit an application but what other documents are required? How long does it take me to obtain my student visa? It is important to plan time to wait for visa processing because the time between finding out I have been accepted to go and leaving may be very close together. Second, do 1 have to present my financial documents; for example proof of funds, to prove that I am able to pay for my education? And last, do I need to obtain the International Certificate of Vaccination? Is it required that I have certain vaccinations before I go? What are they? After all. can you make me a checklist: what I should bring and what I should leave at home? 

I wish you and your family the best. I look forward to hearing from you soon. 

                                                                                                     Regards, 

                                                                                                     Mai Anh

Mong cô duyệt bài ạ:

Dear Duc Son,

Last time I told you that I had been thinking about pursuing higher education in the UK. I got started to learn the process of applying for a university in London some time ago. Now I have some questions for you.

First, what is the procedure for applying for a student visa? Of course. I have to submit an application but what other documents are required? How long does it take me to obtain my student visa? It is important to plan time to wait for visa processing because the time between finding out I have been accepted to go and leaving may be very close together. Second, do 1 have to present my financial documents; for example proof of funds, to prove that I am able to pay for my education? And last, do I need to obtain the International Certificate of Vaccination? Is it required that I have certain vaccinations before I go? What are they? After all. can you make me a checklist: what I should bring and what I should leave at home?

I wish you and your family the best. I look forward to hearing from you soon.

Regards,

Dang Phong

Giải phương trình cos3xcos3x−sin3xsin2x=2−3√28 

Phương trình đã cho <=> (2sinx + 1).(3cos4x +2sinx -4) = 3 - 4(1- sin^2 x) 
<=> (2sinx + 1)(3cos4x + 2sinx - 4) = 4sin^2 x - 1 
<=> (2sinx + 1).(3cos4x + 2sinx - 4) = (2sinx + 1).(2sinx - 1) 
<=> (2sinx + 1).(3cos4x + 2sinx - 4) - (2sinx + 1).(2sinx - 1) =0
<=> (2sinx + 1)(3cos4x + 2sinx - 4 - 2sinx+ 1) = 0
<=> (2sinx + 1)(3cos4x -3) = 0
<=>  (2sinx + 1)(cos4x - 1) = 0
(Đến đây pt tích dễ rồi tự giải nha)

\(sin^2x=cos^22x+cos^33x\)

\(\Leftrightarrow1-cos^2x=2cos^2x-1+4cos^3x-3cosx\)

\(\Leftrightarrow4cos^3x+3cos^2x-3cosx-2=0\)

\(\Leftrightarrow\left(cosx+1\right)\left(4cos^2-cosx-2\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}cosx=-1\\cosx=\frac{1\pm\sqrt{33}}{8}\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=\pi+k2\pi\\x=\pm arccos\left(\frac{1\pm\sqrt{33}}{8}\right)+k2\pi\end{cases}}\left(k\inℤ\right)\)

Có hai lí do giải thích cho dòng đó nha bạn: 

- Do hàm \(cos\)tuần hoàn với chu kì \(2\pi\).

- Tìm chu kì của hàm \(cos\left(4x-\frac{\pi}{6}\right)\)sẽ là giá trị \(T\)dương nhỏ nhất sao cho \(cos\left(4\left(x+T\right)-\frac{\pi}{6}\right)=cos\left(4x-\frac{\pi}{6}\right)\).

Bn vẽ vòng tròn lượng giác ra 

=2 r thì cần j giải

tìm x đóa

ĐK: \(cosx\ne0\Leftrightarrow x\ne\frac{\pi}{2}+k\pi,k\inℤ\).

\(1+tanx=2\left(sinx+cosx\right)\)

\(\Leftrightarrow cosx+sinx=2cosx\left(sinx+cosx\right)\)

\(\Leftrightarrow\orbr{\begin{cases}sinx+cosx=0\\cosx=\frac{1}{2}\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}cosx=cos\left(-x-\frac{\pi}{2}\right)\\cosx=cos\frac{\pi}{3}\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=\pm\left(-x-\frac{\pi}{2}\right)+k2\pi\\x=\pm\frac{\pi}{3}+k2\pi\end{cases}},\left(k\inℤ\right)\)

\(\Leftrightarrow\orbr{\begin{cases}x=\frac{-\pi}{4}+k\pi\\x=\pm\frac{\pi}{3}+k2\pi\end{cases}},\left(k\inℤ\right)\)(thỏa mãn) 

\(1+\tan x=2\left(\sin x+\cos x\right)\)

Bạn áp dụng đẳng thức lượng giác nhé : 

 \(\frac{\sin x+\cos x}{\cos x}=2\sin x+2\cos x\)

Biệt thức : 

\(D=b^2-4ac\)

\(\Leftrightarrow\left(-1\right)^2-4\left(1.1\right)=-3\)

Phương trình không có nghiệm thực : 

\(D< 0\)

Nghiệm tuần hoàn : 

\(2\pi k-\frac{\pi}{4}\)

\(2\pi k+\frac{3\pi}{4}\)

\(2\pi k+\frac{\pi}{3}\)

\(2\pi k-\frac{\pi}{3}\)

              Ps : không hiểu chỗ nào thì bạn hỏi mình nhé, nhớ k :33

                                                                                                                                              # Aeri # 

Để chọn ra một cái quần hoặc một csai áo hoặc một cái cà vạt thì số cách khác nhau là: 

\(C^1_4.C^1_6.C^1_3=4.6.3=72\)(cách) 

13 cách