Mainly is the application of A 2-B 2 = (A-B) (A+B), where both numerator and denominator are multiplied by a number. The steps of these questions are the same. The purpose is to remove the root sign from the denominator. If the denominator in the topic is a number, then both the numerator and denominator are multiplied by the denominator. For example, the multiplication of two (root number 2) equals two, then the root number is gone. If the denominator is added, subtracted, multiplied and divided, for example, "(root number 3)- 1" can be multiplied by "(root number 3)+ 1", which is equal to 3- 1 and 2. I think it's better for you to practice your hands with these questions, so that you won't panic in the exam.