1. Let's clarify the step where $x=3$ was mentioned. 2. To understand where this comes from, we need to see the context or the equation from which $x=3$ is derived. 3. Typically, $x=3$ is found by solving an equation or after simplifying an expression during the solving process. 4. For example, if we had an equation like $$x^2 - 6x + 9 = 0,$$ factoring gives $$(x-3)^2=0,$$ which means $x=3$ is the solution. 5. Please provide the original equation or problem context, so I can give a detailed explanation of how $x=3$ was obtained.