Is 3abc an expression?

yes

Step-by-step explanation:

an expression is like an equation without the equal sign, or according to the Oxford Dictionary: "a collection of symbols that jointly express a quantity."

Yes

Step-by-step explanation:

An expression is a collection of symbols that jointly express a quantity, which means a set of symbols that equals a number. a,b, and c are all variables, meaning that its a expression

a reflection across the x-axis , followed by the by a reflection across the y-axis , and then a scale dilation of 0.5 .

the domain of a function is the set of input values, x , for which a function is defined. the domain is shown in the left oval in the picture below. the function provides an output value, f(x) , for each member of the domain.