Solving Linear Systems—Wolfram Language Documentation

In some cases, however, you may prefer to convert the system of linear equations into a matrix equation, and then apply matrix manipulation operations to solve it. This approach is often useful when the system of equations arises as part of a general algorithm, and you do not know in advance how many variables will be involved.

Source: Solving Linear Systems—Wolfram Language Documentation

Add Transparency to Plots—Wolfram Language Documentation

Transparency is useful in plots when you need an unobstructed view of multiple components of one plot, or simply want to lighten a single plot component against a white background. The Wolfram Language uses the graphics directive Opacity to apply transparency to graphics objects. Opacity can be used with most visualization functions.

Source: Add Transparency to Plots—Wolfram Language Documentation

Loops and Control Structures—Wolfram Language Documentation

The execution of a Wolfram Language program involves the evaluation of a sequence of Wolfram Language expressions. In simple programs, the expressions to be evaluated may be separated by semicolons, and evaluated one after another. Often, however, you need to evaluate expressions several times, in some kind of “loop”. Simple looping constructs. This evaluates Print[i^2], with i running from 1 to 4.

Source: Loops and Control Structures—Wolfram Language Documentation