Step 1 :
Divide $ 8000 $ by $ 3600 $ and get the remainder

$$ 8000 : 3600 = 2 \text{ ( remainder is } \color{blue}{ 800 } \text{ ) } $$

The remainder is positive ($ 800 > 0 $), so we will continue with division.

Step 2 :
Divide $ 3600 $ by $ \color{blue}{ 800 } $ and get the remainder

$$ 3600 : 800 = 4 \text{ ( remainder is } \color{blue}{ 400 } \text{ ) } $$

The remainder is still positive ($ 400 > 0 $), so we will continue with division.

Step 3 :
Divide $ 800 $ by $ \color{blue}{ 400 } $ and get the remainder

$$ 800 : \color{blue}{ \boxed { 400 }} = 2 \text{ ( remainder is } \color{blue}{ 0 } \text{ ) } $$

The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 400 }} $.

This solution can be visualized using a Venn diagram.

The GCD equals the product of the numbers at the intersection.

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