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A repeated expression appears twice in a quadratic equation. What is the useful move?
ASubstitute for the expression
BMultiply out the expression
CDelete one of the two copies
DSquare both sides at once
Answer & Solution
Correct answer: A. Substitute for the expression
1. Some quadratic equations hold the same expression in more than one place.
2. Making a substitution for that repeated expression is often useful.
3. The equation then becomes simpler and much easier to solve.
4. After the new variable is solved, its values are used to find the original variable.
5. Squaring both sides instead would make the equation longer, not shorter.
_Source: Siyavula Mathematics Grade 11 (Everything Maths, CC BY 4.0), Chapter 2: Equations and inequalities_
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