suppose We have some Language L
L is regular => L will support Pumping Lemma
So if language L is not supported by pumping lemma certainly then language is not regular.
so if L supports pumping lemma , no comment
but if L doesn't support pumping lemma , for sure L is non-regular...
so yes! apply pumping lemma and see language didn't support it and you have proved that language can't be regular then....it proves a language non-regular using it's negative result...