While it is always a good idea to check your solutions, it becomes an absolute necessity to do so when dealing with rational expressions or radicals. Because some of the operations that are done when solving equations with rational expressions or radicals are not completely reversible, we may accidentally introduce some "errors" into our calculations. These errors take the form of values that appear to be solutions but are not, usually because they are not within the domain of the original expressions.
When dealing with rational expressions or radicals, you are not finished until you have checked each and every solution found to insure that it is valid.
Note: You must check in the original equation and strictly evaluate!!!