An algebraic expression that always has the same value regardless of the value of the variable is called an identity. An identity, in mathematics, is a relation between A and B that would result to an equality of the two. It should be expressed as A = B wherein both values has some variables that would produce the same value no matter what will be the values used for the two functions. An example would be
5(2x+3)=9x+15+xAssuming x would be 1, when we simplify the equation above, both sides would have the same value of 25. 5(2(1)+3)=9(1)+15+1
25 = 25