The GCD of given numbers is 147.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}294 =& 2\cdot3\cdot7\cdot7\\[8pt]441 =& 3\cdot3\cdot7\cdot7\\[8pt]735 =& 3\cdot5\cdot7\cdot7\\[8pt]\end{aligned}$$(view steps on how to factor 294, 441 and 735. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}294 =& 2\cdot\color{blue}{\boxed{3}}\cdot\color{red}{\boxed{7}}\cdot\color{Fuchsia}{\boxed{7}}\\[8pt]441 =& \color{blue}{\boxed{3}}\cdot3\cdot\color{red}{\boxed{7}}\cdot\color{Fuchsia}{\boxed{7}}\\[8pt]735 =& \color{blue}{\boxed{3}}\cdot5\cdot\color{red}{\boxed{7}}\cdot\color{Fuchsia}{\boxed{7}}\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 3\cdot7\cdot7 = 147 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.