2. Necessary and insufficient conditions

3, c=0( 1, 2, 3 mainly depends on whether the conditions can make the conclusion hold, and vice versa)

(-3,0) and (3,0) (A and B are known from the questions, and C can be given. The focus is on the X axis, so this is the answer. )

Last question, what does point B say? But you only need to establish the standard equation, and then substitute point A and point B into the equation, and you will get a set of quadratic equations with one variable, and then get the answer. Substituting the answer into the original equation is the answer! !