1. The problem is to simplify the expression $x + x$. 2. The formula used here is the distributive property of addition over multiplication: $a + a = 2a$. 3. Applying this rule, we combine like terms: $x + x = 2x$. 4. This means that adding $x$ to itself is the same as multiplying $x$ by 2. 5. Therefore, the simplified form of $x + x$ is $2x$.