( ( The period ) ( ( is ( ( the reciprocal ) ( of frequency ) ) ) . ) )
(ROOT (S (NP (DT The) (NN period)) (VP (VBZ is) (NP (NP (DT the) (NN reciprocal)) (PP (IN of) (NP (NN frequency))))) (. .)))
The period is the reciprocal of frequency.
(ROOT (S (NP (NP (DT The) (NN frequency)) (PP (IN of) (NP (DT a) (NN wave)))) (VP (VBZ is) (NP (NP (DT the) (NN reciprocal)) (PP (IN of) (NP (NP (DT the) (NN period)) (PP (IN of) (NP (DT the) (NN wave))))))) (. .)))