Physics
posted by Stuck .
"Point S1 and S2 are close sources of circular water waves each of wavelength 6.0cm. P is a point some distance away from the sources. Explain whether the following path differences (path difference = PS2  PS1) result in nodes or antinodes.
a) 6.0cm
b) 9.0cm
c) 18cm
d) 21cm"
I am very confused. What am I supposed to do?

if the path length is a multiple of a wavelength, reinforcement (antinode) occurs, if it is a odd number of halfwavelengths, it is destructive and a node results.
for instance d) Not a multiple of 6cm, but it is ...18+3 or 6*3+3 which means it is a halflength left over, destructive. 
Ah! Thank you so much!