Are a rational expression and its simplified forms equivalent? provide mathematical examples

Yes. 

For example, 100/50 = 10/5 = 2

A rational number is any number or numerical value which can be possibly stated in a fraction form of numbers, it basically has a numerator and denominator. Furthermore, the values of the numerator and denominator is integers and doesn’t equal to 0. In this given case of 8 over 5 or 8/5 this fractional number can still be expressed in a standard numerical form with a decimal as 1.6 without repeating decimal values.