Explanation
Trend lines have become popular questions in recent Tableau examinations. Follow along:
1) First drag Sales to the Rows shelf and Profit to the Columns shelf:

c
You will only see a single mark since the view is aggregated.
2) Now, break down this view by state. Drag State into Detail on the Marks shelf ( or directly to the view):

3) Finally, move to the Analytics pane, and drag Trend line to the view. When you drag it, select the Linear option!:


4) The following is our view. Hover over the trend line to see the R-squared value:

Explanation
According to the official Tableau documentation:

Dimensions don't have aggregation properties, and adding properties manually each time defeats the whole DEFAULT aggregation purpose. Window tab doesn't have any default aggregation option!

Explanation
The data that you analyze in Tableau is often made up of a collection of tables that are related by specific fields (that is, columns). Joining is a method for combining data on based on those common fields. The result of combining data using a join is a virtual table that is typically extended horizontally by adding columns of data.
For example, consider the following two tables originating from a single data source:

We can combine these 2 tables, simply by joining the tables on ID to answer questions like, "How much was paid in royalties for authors from a given publisher?". By combining tables using a join, you can view and use related data from different tables in your analysis.

Explanation
From the official documentation, the following are the major advantages of using Tableau Data Extracts:

From Tableau 2020.2 onwards, .hyper is the recommended way since it is faster than .tde!

Explanation
SUM is an aggregate function, not a table calculation!
A table calculation is a transformation you apply to the values in a visualization. Table calculations are a special type of calculated field that computes on the local data in Tableau. They are calculated based on what is currently in the visualization and do not consider any measures or dimensions that are filtered out of the visualization.
The most common Table calculations are:
Running Total
Percent Difference
Difference
Percent of Total
Rank
Percentile


These can be calculated using : Table(across), Cell, or Specific dimensions!