“If the result is correct...”.
There’s only one correct result to two numbers multiplied. How will they know it’s correct?
If the proof is correct, if the resulting algorithms work. One could apply the results to problems that are practical to solve and check for consistency with methods currently in use. That still does not formally prove that the method is correct, any more than the observation that 3, 5 and 7 are all prime proves all odd numbers are prime, it only proves that we have not yet discovered any counterexamples.
Using long form
“How will they know it’s correct?”
Like many of us who took high school math, we had to show our proof, unlike me who usually answered choice C and had a 25% chance the answer was correct.