The GCD of given numbers is 14.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}28 =& 2\cdot2\cdot7\\[8pt]294 =& 2\cdot3\cdot7\cdot7\\[8pt]\end{aligned}$$(view steps on how to factor 28 and 294. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}28 =& \color{blue}{\boxed{2}}\cdot2\cdot\color{red}{\boxed{7}}\\[8pt]294 =& \color{blue}{\boxed{2}}\cdot3\cdot\color{red}{\boxed{7}}\cdot7\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 2\cdot7 = 14 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.