The total number of items in the series is the number of items in the series. An infinite sequence has no items. In the words of A Brief History of Mathematics, mathematics is a science that studies various structures (relationships) on sets. It can be seen that mathematics is an abstract subject, and rigorous process is the key to mathematical abstraction.

Mathematics plays an irreplaceable role in the development of human history and social life, and it is also an indispensable basic tool for studying and studying modern science and technology.

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The establishment of a quadratic equation must be satisfied at the same time: it is an integral equation, that is, both sides of the equal sign are algebraic expressions, if there is a denominator in the equation; The unknown is in the denominator.

Then this equation is a fractional equation, not a quadratic equation. If there is a root sign in the equation and the unknown is within the root sign, then the equation is not a quadratic equation (it is an irrational number equation).