To determine which of the given quadratic equations can be solved by grouping, we need to look for a way to factor each equation into pairs that can be grouped together.
Let's analyze each equation:
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\(x^2 + 10x + 21 = 0\)
- Factors as \((x + 3)(x + 7) = 0\).
- This equation cannot be solved by grouping as it does not require grouping.
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\(x^2 + 8x - 22 = 0\)
- Look for two numbers that multiply to \(-22\) and add to \(8\). The numbers \(11\) and \(-2\) work. So it can be factored to \((x + 11)(x - 2) = 0\).
- However, it's again not a case for grouping.
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\(x^2 - 4x - 8 = 0\)
- Look for two numbers that multiply to \(-8\) and add to \(-4\). The numbers do not easily factor, suggesting it is not a grouping case.
-
\(x^2 - 12x + 18 = 0\)
- Look for two numbers that multiply to \(18\) and add to \(-12\). The numbers would be difficult to find; hence it does not suit grouping well.
To perform grouping effectively, we typically look for a polynomial that can be rearranged into two parts that share common factors. None of these quadratic equations seem to fit easily into a grouping method directly, as they either do not factor nicely or do so in a way that does not involve grouping.
Nevertheless, if we had to choose the one most likely aligning with the grouping method (with a small potential of manipulating into two grouped factors), it would probably be this one:
\(x^2 - 4x - 8 = 0\)
It is the easiest case where the expression could lead to further calculations to get simpler factors when possible, such as completing the square or similar method, should be considered for that analysis.
So, the correct answer using guidance on common factors while assessing for potential grouping would lead me to tentatively give:
\(x^2 - 4x - 8 = 0\) as closest to suit consideration for solving through grouping.
However, note that truly effective grouping methods would be more apparent in higher degree polynomials.