Question 1161878
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cos(a)*cos(b) = {{{(1/2)*cos(a-b)}}} + {{{(1/2)*cos(a+b)}}}.


There are two harmonic modes in this instrument.


The low frequency is {{{(1000-20)/2}}} Hertz = 490 Hertz;  the period is  {{{1/490}}} of a second.


The high frequency is {{{(1000+20)/2}}} Hertz = 510 Hertz;  the period is  {{{1/510}}} of a second.


The amplitude is 4 units for each harmonic mode.
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