Two or more expressions are equivalent expressions if they have the same result when evaluated. In the case of numerical expressions, two equivalent expressions result in the same number when evaluating the operations.
12−62⋅3=6=6
Since both 12−6 and 2⋅3 equal 6, these expressions are equivalent. In a similar way, two algebraic expressions are equivalent if both expressions result in the same number for every value of the variables.
y+42+y+2
In both of these expressions, any value for y results in the same number. For example, substitute 5 for y.