( ( If ( we ( ( multiply ( the frequency ) ) ( by ( the wavelength ) ) ) ) ) ( we ( ( obtain ( ( the speed ) ( of ( the wave ) ) ) ) . ) ) )
(ROOT (S (SBAR (IN If) (S (NP (PRP we)) (VP (VB multiply) (NP (DT the) (NN frequency)) (PP (IN by) (NP (DT the) (NN wavelength)))))) (NP (PRP we)) (VP (VBP obtain) (NP (NP (DT the) (NN speed)) (PP (IN of) (NP (DT the) (NN wave))))) (. .)))
If we multiply the frequency by the wavelength we obtain the speed of the wave.
(ROOT (S (NP (NP (DT The) (NN product)) (PP (IN of) (NP (NP (NP (DT a) (NN wave) (POS 's)) (NN wavelength)) (CC and) (NP (PRP$ its) (NN frequency))))) (VP (VBZ is) (NP (PRP$ its) (NN speed))) (. .)))