The GCD of given numbers is 2.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}12 =& 2\cdot2\cdot3\\[8pt]2 =& 2\\[8pt]\end{aligned}$$(view steps on how to factor 12 and 2. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}12 =& \color{blue}{\boxed{2}}\cdot2\cdot3\\[8pt]2 =& \color{blue}{\boxed{2}}\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 2 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.