Answer: our function is:
f(x) = A*sin(2*pi*270s*x)
Step-by-step explanation:
We have that the frequency of a given engine is 270 hz, it starts at 0, so we may represent this with a sin function (because sin(0) = 0)
Then we could use the function
f(x) = A*sin(c*x)
A is the maximum intensity of the hum, and c depends on te frequency, we know that the period of a sin function is 2pi, then:
f = 270/s
T = 1/270s
c*1/270s = 2pi
c = 2*pi*270s
Then our function is:
f(x) = A*sin(2*pi*270s*x)