That type of sentence is called a mathematical expression.
It is an expression.
It is evaluating the expression.
That sounds like the definition for Recursive Formula.
Constants (numbers), variables, the four basic operations of arithmetic (+, -, *, /) as well as brackets and indices (including negative and fractional ones).
A proportion is simply a ratio of one number to another. An equation can be any or all of the mathematical operations taking place on numbers or variables.
They are terms of an expression or an equation
algebraic equation
It is an expression.
the order of operations
Algebraic expressions is a mathematical phrase that contains operations numbers or variables.
Numerical Expression
It is an expression.
an expression
order of operations
An expression.
Expression
An Algebraic Expression.