The above problem is that the range of a becomes a necessary and sufficient condition of M∩P (that is, the range of a is a necessary and sufficient condition of M∩P), so M∩P can derive the range of a (a necessary condition) and M∩P () is a necessary and sufficient condition that the range of a cannot be derived.

And want a range can't push out M∩P, then a.

When necessary (small scope can be extended to large scope)

Therefore, the range of M∩P {x | 5 < x ≤ 8} is less than {x | 5 < x ≤ 8 or a ≤ x ≤-3}, so it is necessary to expand the small range to a large range.