Do not you think that a math formula is right or do you doubt any statement of a theory? Here you can eliminate your scientific doubt by formal reasoning (mathematical proofs, derivations) or empirical reasoning (experiments, studies).
Derivation of the velocity formula for the elastic head-on collision of two different masses using conservation of momentum and conservation of energy.
Derivation of the Heisenberg uncertainty relation for momentum and position using a single slit through which many electrons pass and for which the De Broglie relation holds.