How to Solve Quadratic Equations

Quick answer

To solve quadratic equations, first classify the problem, preserve the meaning of every transformation, and verify the final result in the original statement. For the worked example x^2 - 5x + 6 = 0, the result is x = 2 or x = 3. The method below shows why that result follows rather than presenting it as an unexplained calculator output.

Identify the problem before calculating

A quadratic equation can be arranged as ax² + bx + c = 0 with a nonzero. The discriminant b² - 4ac predicts whether real roots are distinct, repeated, or absent. This classification step matters because a familiar-looking expression can require a different rule when its structure changes. Write down any domain restriction, unit, dimension, or reference value before manipulating the symbols.

Keep every transformation reversible. An algebraic line is not merely formatting: it is a claim that the solution set has not changed. Record restrictions before cancelling factors or applying inverse operations.

Step-by-step method

1. Move every term to one side so the other side is zero.
2. Look for a common factor or an easy factor pair.
3. If factoring is not practical, use completing the square or the quadratic formula.
4. Keep both plus and minus branches when a square root appears.
5. Substitute each candidate root into the original equation.

Each line should answer two questions: what operation was performed, and why that operation preserves or correctly changes the mathematical object. When a calculator or browser tool is used, keep the original input visible so the output can be compared with the source problem.

Worked example

1. For x² - 5x + 6 = 0, find two numbers with product 6 and sum -5.
2. The numbers are -2 and -3, so factor as (x - 2)(x - 3) = 0.
3. Set each factor equal to zero: x = 2 or x = 3.
4. Both substitutions make the polynomial equal zero.

The result x = 2 or x = 3 is not accepted solely because it looks plausible. The example retains the intermediate quantities that make a sign, denominator, exponent, dimension, or rounding mistake visible.

Read the visual explanation

The three diagrams on this page separate the concept, the execution sequence, and the final check. Use the concept diagram to recognize the structure, the workflow diagram while solving, and the verification diagram after obtaining a candidate result. The diagrams are SVG files, so text remains selectable and the graphics stay sharp on mobile screens and when printed.

Common mistakes

• Forgetting one root after factoring.
• Using the quadratic formula with the wrong sign for b.
• Rounding a root before the final verification.

A reliable correction strategy is to return to the earliest line where the mathematical object changed. Repeating only the final arithmetic often reproduces the same hidden setup error.

Verify the result

The residuals 2² - 5(2) + 6 and 3² - 5(3) + 6 are both zero. Also inspect whether the answer has the correct sign, scale, units, dimension, and domain. For an equation, substitution is decisive. For an inverse pair such as differentiation and integration, apply the inverse operation. For a statistical or financial result, recompute one intermediate quantity and compare it with an independent method.

Use the tool without losing the reasoning

Open the matching browser tool with the worked input when available. The tool is useful for recomputation and output formatting, but the page's decision rule remains necessary: unsupported expressions, ambiguous units, and incorrect assumptions can produce a neat result that answers a different question.

Keep a compact record containing the original problem, the selected method, intermediate values, the final result, and the verification. That record is more useful for study, teaching, and debugging than an isolated answer.

Visual explanation