Common errors in quadratic formula substitution
These are mistakes made while substituting a, b, and c into the quadratic formula, especially sign mistakes and denominator mistakes.
Practice This ConceptMain explanation
Teacher explanation
The formula is reliable only when the values are copied correctly. Many wrong answers come from writing b with the wrong sign, forgetting ±, or using 2 instead of 2a.
Example
For 2x^2 - 4x + 3 = 0, the denominator must be 2a = 4, not just 2.
Simple analogy
Copy signs as they are, then solve.
Common confusion
Students often change b from -4 to +4 or forget that the denominator depends on a.
Exam tip
Write a, b, and c separately before starting the formula; do not substitute in a hurry.
Answer writing and exam use
1-mark use
Write the exact meaning of common errors in quadratic formula substitution in one clean line.
2-mark use
Define common errors in quadratic formula substitution and add one example or condition.
3-mark use
Explain common errors in quadratic formula substitution, show the method or example, and mention the common mistake.
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