Create a model to answer questions

The answer is 1 4

First, turn all the cos into sin

(sin 2) 74° + (sin 2) 76° - root number 3*sin74°*sin76° is obtained

sin^2)74°+(sin^2)76°-2cos30°*sin74°*sin76°

If you know the sine theorem and the cosine theorem, then you can see the answer directly.

Upstairs substituted the cosine theorem, why not substitute the sine theorem a=2r*sina, and the answer can be directly obtained is sin 30°=1 4

But in fact, the landlord means that these formulas are not allowed to be used, and neither of them can be used. But with one, why not use the second.

It is suggested that the landlord may wish to take a look at the proofs of the sine theorem and the cosine theorem, as well as the formula.

with a calculator. If that doesn't work, draw an approximate image.

Some simple examples in Figure 1-1 show some classic algorithms and data structures (more basic). Modeling a problem is to abstract the problem you want to solve, transform it into a basic data structure, and then apply the corresponding algorithm.

The process mentioned above is essentially the essence of learning algorithms and data structures. Abstract and decompose the problem and transform it into the corresponding basic content. In particular, it can be broken down into classic problems that have already been solved.

The part that I didn't understand was why I had to learn algorithms and data structures. The reason for this is not only that the purpose of learning is not right, but also that there is no problem environment for me to operate.

The next section lists some of the underlying data structures that the algorithms associated with them query on their own. The data structure referred to here should be an abstract mathematical concept, similar to and different from the previous algorithm books, and should not be understood from the spatial organization in memory.

The original reason for reading this material was my confusion about the data preprocessing part of machine learning; But after reading this material, I realized that I had found something wrong, and the part I cared about should be the content of the data analysis part. Of course, I also have to learn the algorithm myself, so I read this part of the content).

For this part, if I want to organize the language myself, I might as well use the ** in the book directly. ）

These data structures are some basic content, and I have read these books many times in the past, among which there are more trees and graphs, but I have not mastered them. The title of this section of the Algorithm Design Handbook is Composite Objects; There is also a subsection, called Recursive Objects, which is actually the focus of many book introductions, and it is a pity that they do not really explain the role of recursion when they introduce it, which is not as easy to understand as this part of the book as Youbi.

Personally, I think that recursion has two functions, one is the form in which the data is organized, and the other is the principle in the operation of the algorithm.

There isn't much of a key thing in problem modeling, but rather the idea that it lists a large library of data types that practitioners can match to their applications. Don't be afraid when you can't match. I think any problem can be roughly broken down into these basic contents, and if it is matched, it can be further broken down to achieve the purpose.

Completed on 2018 11 27).

There need to be a lot of subjects when modeling, and once you have a model, you can't just focus on the subjects you care about.

When building a model, there are often many different subjects and variables that need to be considered, and it is important to ensure that the model has sufficient complexity and applicability. However, when working with a model, you can choose to focus only on specific subjects or variables to suit your specific needs. For example, if you're building a sales** model in a rubber lift, you may want to consider multiple variables such as product type, customer attributes, market trends, and more.

However, when you actually use the model, you may only analyze certain product types or customer attributes, as this is more important to your business decisions. As a result, there are many subjects and variables to consider when modeling, but when working with a model, you can choose which ones to care about depending on the situation. This will better meet your needs while ensuring the reliability and validity of your model.