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由实数的性质不难得出“xy=0”与“x=0或y=0”等价;而“x~2+y~2=0”与“x=0且y=0”等价,仅一字之差。再看看它们做为曲线方程的几何意义,却失之千里,前者表示两条相交直线x=0和y=0;而后者只表示一个点(0,0).可见正确理解和应用关连例“或”与“且”是十分重要的。“且”是表示并列关系的连词,前后两项是并存的,缺一不可;而“或”则是表示不定的连词,有选择的关系,前后两项中至少选一.
From the nature of real numbers, it is not difficult to find that “xy=0” is equivalent to “x=0 or y=0”; and “x~2+y~2=0” is equivalent to “x=0 and y=0”. Only one word difference. Let’s take a look at the geometric meaning of these equations as curves, but they are lost. The former represents two intersecting lines x=0 and y=0; the latter only represents one point (0,0). It can be seen that the correct understanding and application examples “Or” and “and” are very important. “And” is a conjunction that represents a tie, both before and after the coexistence, are indispensable; and “or” is an indefinite conjunction, a selective relationship, at least one of the two before and after the election.