To determine the missing step in proving the equivalence of \(12a + 10 + a = 10 + a + 12a\), we can apply the Commutative Property, which states that the order of addition can be changed without affecting the sum.
We start with the left-hand side of the equation:
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Step 1 (missing): \( 12a + 10 + a = 10 + 12a + a \)
- (This step uses the Commutative Property to rearrange terms.)
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Step 2: \( 10 + 13a = 10 + 13a \)
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Step 3: The expressions are equivalent because they both equal the same value.
So, the missing step is \( 12a + 10 + a = 10 + 12a + a \). This reflects the use of the Commutative Property.