I need help with the interference of sound waves...Please!!?

Question

A pair of speakers separated by 0.700 m are driven by the same oscillator at a frequency of 681 Hz. An observer, originally positioned at one of the speakers, begins to walk along a line perpendicular to the line joining the speakers. (Assume the speed of sound is 345 m/s.)
(a) How far must the observer walk before reaching a relative maximum in intensity?
_______ m
(b) How far will the observer be from the speaker when the first relative minimum is detected in the intensity?
_______m

Answer 1

Basically you have two signals, one from the farther speaker traveling along the hypotenuse C and one from the nearer speaker along a side A of a right triangle. The third side B is between the speakers and is 0.7 m. Side A is the variable to solve for. Find the wavelength L (345/681 m) and then find the minimum value of A where the hypotenuse = A + an integer * L. This is the first reinforcement or maximum point. Then find the minimum value of A where the hypotenuse = A + an odd integer * 0.5L. This is the first cancellation or minimum point.
You can solve for using the Pythagorean theorem. E.g.,
A^2 + B^2 = C^2
For (a), A^2 + 0.7^2 = (A+(i*L))^2, i=1,2,3...
For (b), A^2 + 0.7^2 = (A+(i*0.5L))^2, i=1,3,5...
Just do the algebra. The above is a generalized procedure for finding the first maximum and minimum, but in this problem, since the difference between C and A must be less than B which roughly = 1.4L, you can expect the solutions for the maximum and minimum when i=1.