The first step in simplifying a rational expression is to determine the domain, the set of all possible values of the variable. The denominator in a fraction cannot be zero because division by zero is undefined. So we need to figure out what values of the variables in the expression would make the denominator equal zero.these values cannot be included in the domain,so they called excluded values. We discard them right at the start, before we go any further.
Once we’ve figured out the excluded values, the next step is to simplify. To simplify a rational expression, we follow the same approach we’d use to simplify numerical fractions: find common factors in the numerator and denominator.
