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Quadratic Formula

一元二次方程求根公式

x=2a−b±b2−4ac​​

Theoretical Identity Description:

Solves quadratic equations of the form ax² + bx + c = 0. Here, 'x' represents the roots, 'a', 'b', and 'c' are coefficients, and the term under the square root (b² - 4ac) is the discriminant.

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Rigorous Derivation Tree

4 Logical Steps
Step 1check_circleValid Deduction
ax2+bx+c=0⟹x2+ab​x=−ac​(a=0)

Divide through by leading coefficient 'a' and move constant term to the right-hand side.

Step 2check_circleValid Deduction
(x+2ab​)2=4a2b2​−ac​=4a2b2−4ac​

Complete the square by adding (b / 2a)² to both sides of the equation.

Step 3warningCommon Fallacy
x+2ab​=2ab2−4ac​​

Take the square root of both sides to isolate the linear binomial.

Correct Rule:Algebraic Square Root Invariant: √z² = ±z
Step 4check_circleValid Deduction
x=2a−b±b2−4ac​​

Subtract b / (2a) from both sides with correct ± sign.

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CSCA Exam Triggers & Traps

High-Yield Exam Focus
psychologyProblem Pattern Recognition

Use when factoring by inspection is non-trivial, or when finding roots and discriminant Δ = b² - 4ac conditions.

errorCommon Examination Pitfalls

Ensure equation is strictly in standard form ax² + bx + c = 0 before extracting coefficients a, b, c.

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Related Formulas in Sets & Inequalities

6 Formulas
Quadratic Formula
一元二次方程求根公式
Union of Sets
集合的并集
Intersection of Sets
集合的交集
Complement of a Set
集合的补集
Rational Inequality Equivalence
分式不等式的等价转化
AM-GM Inequality
基本均值不等式

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