#2. Because for all the other ones you have to make it equal to zero and this is how you solve #2 using square root property. When you have ax^2+c=0 where c >0, you can then use square root property. You don’t have to make it equal to zero if it has something like x^2-3=6 or something. Like a constant at the end and an x^2 at the beginning. Hope this helps!!! Let me know if you have questions
