Final answer:
If a and b are positive integers and a+b is even, then both a and b must be even.
Step-by-step explanation:
In mathematics, if a and b are positive integers such that a+b is even, then both a and b are even. This can be proven using the fact that if we assume a and b are odd, then a+b would be odd. However, we are given that a+b is even, so our assumption is false and a and b must both be even.