( ( Useful ( ( ( Web ( Links Frequency ) ) and ) ( Period ( of ( a ( Wave 18 ) ) ) ) ) ) . )
(ROOT (S (VP (VB Useful) (NP (NP (NNP Web) (NNP Links) (NNP Frequency)) (CC and) (NP (NP (NN Period)) (PP (IN of) (NP (DT a) (NNP Wave) (CD 18)))))) (. .)))
Useful Web Links Frequency and Period of a Wave 18.
(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))))))) (. .)))