📚 Simplifying and Operating Algebraic Fractions | 代数分式的化简与运算
Algebraic fractions appear throughout A-level mathematics, from solving rational equations to evaluating limits in calculus. This guide covers the key techniques for simplifying and performing the four basic operations on algebraic fractions, along with important domain restrictions and common exam pitfalls.
代数分式贯穿 A-level 数学的始终，从解有理方程到微积分中计算极限都会用到。本指南系统讲解代数分式的化简以及加减乘除四则运算的关键技巧，同时强调重要的定义域限制与常见考试陷阱。
1. Understanding Algebraic Fractions | 理解代数分式
An algebraic fraction is a quotient of two algebraic expressions, usually polynomials. For example, (x + 2)/(x² − 1) is an algebraic fraction because the numerator x + 2 and the denominator x² − 1 are both polynomials.
代数分式是两个代数表达式（通常是多项式）的商。例如，(x + 2)/(x² − 1) 是代数分式，因为分子 x + 2 与分母 x² − 1 都是多项式。
A proper algebraic fraction has numerator degree less than denominator degree; an improper fraction can be rewritten by division. However, for simplification and operations, the same fraction rules apply.
如果分子的次数低于分母的次数，称为真分式；否则为假分式，可先做多项式除法。不过，无论真假分式，化简与运算的基本规则都相同。
Why does this matter? Algebraic fractions behave like numerical fractions, but the presence of variables means we must always consider the values that make the denominator zero.
为什么这一点很重要？代数分式的行为与数字分数类似，但变量存在意味着我们必须始终关注使分母为零的那些取值。
2. Domain and Excluded Values | 定义域与排除值
An algebraic fraction is undefined when its denominator equals zero. These forbidden values must be excluded from the domain.
当分母等于零时，代数分式无定义。这些不允许的取值必须从定义域中排除。
(x + 1)/(x − 3) is undefined when x − 3 = 0, so x ≠ 3
(x + 1)/(x − 3) 在 x − 3 = 0 时无定义，因此 x ≠ 3
For a denominator that factors, each factor contributes an excluded value.
当分母可以因式分解时，每一个因子都对应一个排除值。
