Answer:
GCD(a,b) is multiple of d. It means d divides GCD(a,b).
Step-by-step explanation:
Let a and b are two unknown numbers.
If d divides a and d divides b, then a and b are multiple of d.


where, m and n are integers.
The greatest common divisor of a and b is


GCD(a,b) is multiple of d. It means d divides GCD(a,b).
Hence proved.