Destructive interference, two speakers

[skyline_2k7]

Homework Statement

Two speakers 14 m apart are emitting tones at a frequency of 1020 Hz. What is the
closest distance (in m) from one speaker, along the line connecting the speakers, at
which the sound intensity be will be zero?

Homework Equations

V= Lambda x f

The Attempt at a Solution

i tried this so far, but i don't have the correct answer. (it is .5 m)

l________________________________l
14m
l______l
x (minimum distance x, not known)

L2-L1= 14-x-(x)
Delta L= 14-2x

Lambda =v/f
lambda = (343 m/s) / 1020 Hz

lambda= .33627 m.

i don't know what to do now. Please help me

 

[Redbelly98]

There is a condition on ΔL in order to have destructive interference:

ΔL = {something having to do with wavelength}​

Use that relation, and the fact (you derived) that ΔL=14-2x, to find possible values for x.