A formula or an expression.
It would be a formula.
geometry
operators
No, it is not a mathematical term.
a equation
Probability
significant digits
The answer to the calculation is simply called the square root.
Tactical Call Signs
I don't know what a 'mathematical' sentence is. I'd prefer to call it an English sentence that describes a mathematical process and makes a statement concerning mathematical matters.
This is a mathematical "expression".
Mathematicians call them "factor pairs."
Algorithm