The GCD of given numbers is 64.
Step 1 :
Divide $ 128 $ by $ 64 $ and get the remainder
The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 64 }} $.
We can summarize an algorithm into a following table.
| 128 | : | 64 | = | 2 | remainder ( 0 ) |
| GCD = 64 | |||||
This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.