The quantity ω(x):= limsup_T->+infinity Pi/T*ν(x,T) is said to be the frequency of a function x:[0,infinity)->R,
where ν(x,T) equals the number of zeros (taking into account the multiplicities) of the function x on the interval [0,T].
a) To estimate from above the frequency of any non-zero solution of the ODE diff(x(t),t$2011)+x(t)=0.
b) To find the frequency of the function x(t):=sin(t)+sin(Pi*t).
Edit. In the second entry ν(x,t) was replaced by ν(x,T).
