Generally, y is used to represent the unknown, which can directly enter the original equation. Like x and z, it can represent numbers.

Binary linear equation:

There are two unknowns called binary linear equations, such as: x+y=5 and x-y=3.

Three-dimensional linear equation:

There are three unknowns, such as x+y+z= 10 and x+y-z=6.

The significance of Yuanhe times:

How many unknowns are there in the meta-index; Degree, representing the exponent of the highest term of the unknown in the equation.