Question 867377
During an experiment, the intensity i(t) of the electric current of a device as a function of time t elapsed since the beginning of the experiment is given by: 
i(t)=6sin((pi*t/12)+(2*pi/3)+6 
The device emits a sound signal each time the current’s intensity is equal to 9.
The experiment lasts 120 seconds.
How many sound signals does the device emit during the experiment? 
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Period = (2pi)/(pi/12) = 24 seconds
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Phase shift = -c/b = -[(2pi/3)/(pi/12)] = -8
# of periods in 120 sec = 120/24 = 5
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Since the range of "i" is [0,12] i will equal 9 twice during
each cycle.
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# of alarms = 10
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{{{graph(400,400,-20,120,-10,20,6sin((pi/12)x + (2/3)pi)+6),9}}}
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Cheers,
Stan H.
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