A right triangle and a student's process for finding the length of the unknown side of the right triangle are given as follows. Based on the information given, which of the following skills is the most important to review with this student?
1) Solving for a variable in a quadratic equation
2) Finding the approximate value of a square root
3) Determining whether a triangle is a right triangle
4) Identifying which side of a right triangle is represented by each variable in the Pythagorean theorem