The GCD of given numbers is 207.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}414 =& 2\cdot3\cdot3\cdot23\\[8pt]1035 =& 3\cdot3\cdot5\cdot23\\[8pt]\end{aligned}$$(view steps on how to factor 414 and 1035. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}414 =& 2\cdot\color{blue}{\boxed{3}}\cdot\color{red}{\boxed{3}}\cdot\color{Fuchsia}{\boxed{23}}\\[8pt]1035 =& \color{blue}{\boxed{3}}\cdot\color{red}{\boxed{3}}\cdot5\cdot\color{Fuchsia}{\boxed{23}}\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 3\cdot3\cdot23 = 207 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.