How many nodal lines for two point sources at 2.5 lamda separation?

[MaryCate22]

Homework Statement

How many nodal lines are created by two point sources emitting at the same wavelength that are separated by a distance equal to 2.5 lamda?

Homework Equations

My textbook says, "If two coherent sources located a distance d apart emit identical waves of wavelength lamda, then the number of nodal lines on either side of a straight line running through the centers of the sources is the greatest integer smaller than or equal to 2(d/lamda)."

The Attempt at a Solution

Using the formula from the textbook I get 5 nodal lines. But this answer is incorrect. I've also tried 3 based on the fact that nodal lines occur in places where the path difference from the sources are some 0.5 lamda, 1.5 lamda, 2.5 lamda,... etc. I'm thinking based on the quote from the textbook that I need to double my answer of five since the answer is just for one side of a line running through the center of the sources. I really don't want to lose anymore credit however. Any hints?

 

[MaryCate22]

Never mind you guys, I solved it. N=10 was in fact the correct answer. Sorry y'all.