A radical equation is one in which the unknown variable (e.g. $x$) is under the radical sign. For example:
When it comes to solving radical equations, oftentimes your teacher will expect you to check your answer using the original equation. This involves substituting your answer back into the equation to verify whether the left and right side are the same. If they are not the same, then no solution exists. An example of this is illustrated in Example 2 of the video below.