Can you help me with this queation?

Find the resultant amplitude when 8 harmonic oscillations are superimposed, each one having the same frequency and amplitude but with phases differing by 15 degree steps. For what value of the phase difference would the result be zero?

Answers:
ra when 8 ho are superimposed @ ~ excuse me please!
sorry, i am not THAT CLEVER!!
y=Asin((omega)t-+kx)

use this formula to find each's amplitude and total it up.

omega is the angular speed, k is the wave number
I haven't worked it out on paper but I think that if the phase difference was 45 deg the total would be flat (or maybe even any multiple of 45 - no that can't be right - but certainly would work for 180 deg - sketch it to see why)
If the magnitudes are equal, as well as the phase differences, then you can construct a vector diagram which will be a part of a regular polygon. The formula is given by
A' / A = sin( N*Phase diff/2) / sin (Phase diff/2 )
where A' = magnitude of the resultant vector
A = magnitude of the given vector
N = the no. of vectors to be added
In your case : A' / A = sin 60 / sin 7.5 = 6.63

To get zero resultant vector, the numerator must be zero.Hence N* (Phase diff/2) = 180.
N*15/2 = 180.
N = 180*2/15 = 24

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