Simplify the following text for a Grade 3 native English-speaking person.
Original: A cosine wave is said to be `` sinusoidal '' , because which is also a sine wave with a phase-shift of Ï \/ 2 . Because of this `` head start '' , it is often said that the cosine function leads the sine function or the sine lags the cosine .
Simplified: This is a picture of a sine wave .