Final answer:
The property used to rewrite the expression log2 10 + log2 4 = log2 40 is the addition property of logarithms.
Step-by-step explanation:
The property used to rewrite the expression log2 10 + log2 4 = log2 40 is the addition property of logarithms. According to this property, the logarithm of the product of two numbers is equal to the sum of the logarithms of the individual numbers.
In this case, we have log2 10 + log2 4. Using the addition property, we can rewrite it as log2(10 * 4) = log2 40.
Therefore, the property used to rewrite the expression is the addition property of logarithms.