A is indeed contained in B, that is to say, set A is in set B, but it cannot overlap. Therefore, 2-a≥-3, 2+a≤5, a>0. But you can only take one equal sign. Otherwise, it is not really included! Because set a is also ">" No, even if it is a=-3 here, the value of x in set a is-1.

Solution: note that b = {x │-3 5, so 2-a >-3①; When 2+a=5, 2-A =- 1 >-3, which satisfies that A is the proper subset of B, so 2+A ≤ 5②; a > 0③； The final solution is: 0 < a ≤ 3.

Mathematics is a universal means for human beings to strictly describe the abstract structure and mode of things, and can be applied to any problem in the real world. All mathematical objects are artificially defined in essence. In this sense, mathematics belongs to formal science, not natural science. Different mathematicians and philosophers have a series of views on the exact scope and definition of mathematics.

Development history

Mathematics (hanyu pinyin: shùXué；; ; Greek: μ α θ η μ α κ; English: mathematics or maths), whose English comes from the ancient Greek word μθξμα(máthēma), has the meaning of learning, learning and science. Ancient Greek scholars regarded it as the starting point of philosophy and the "foundation of learning".

Its plural form in English and the plural form in French plus -es form mathématiques, which can be traced back to the Latin neutral plural (mathematica), and Cicero from the Greek plural τ α μ α θ ι α ι κ? (ta mathē matiká).