Your question refers to "these" mathematical expressions. In such circumstances would it be too much to expect that you make sure that there is something that is "these" could refer to?
It is a more complicated mathematical expression.
Yes, a mathematical expression can have no variables, but such an expression is usually not very useful. An example of a valid expression without variables is: 1+1=2
It means "a Mathematical Expression".
Average speed can be represented by the mathematical expression "distance x time."
CPUs, when given mathematical equations, apply the laws of mathematics to those equations. The equation a = a is true by the reflexive property of equality.
EQUATION
It is called "to evaluate" the expression.
A mathematical expression is a collection of numbers and variables along with mathematical operators - other than equalities or inequalities.
Any "expression" that represents a numeric value. Example: 2+2=4 or x+7=10. Actually the examples above are equations, not expressions. Expressions do not have = signs. 7a and 4x are examples.
formula
a formula
Square root is a mathematical function whose argument needs to be a mathematical quantity or expression. Since helium is neither a mathematical quantity nor an expression, the question makes no sense.