( ( ( ( Find ( ( the difference ) ( between ( the ( two ( individual frequencies ) ) ) ) ) ) and ) ( ( compare this ) ( to ( the ( beat frequency ) ) ) ) ) . )
(ROOT (S (VP (VP (VB Find) (NP (NP (DT the) (NN difference)) (PP (IN between) (NP (DT the) (CD two) (JJ individual) (NNS frequencies))))) (CC and) (VP (VB compare) (NP (DT this)) (PP (TO to) (NP (DT the) (NN beat) (NN frequency))))) (. .)))
Find the difference between the two individual frequencies and compare this to the beat frequency.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NNS waves)) (PP (IN of) (NP (CD two) (JJ different) (NNS frequencies)))) (VP (VBP interfere)))) (, ,) (NP (NN beating)) (VP (VBZ occurs)) (. .)))