---

X_k = sum from {n=0} to {N-1} {x_n cdot exp left({-2 cdot %pi cdot i cdot k cdot n} over {N} right)}
newline
f_k = {k cdot f_d} over {N}
newline
A_k = {2 cdot abs {X_k}} over {N}, ~~ 0 < k < {N} over {2}
newline
%phi_k = "arg" left(X_k right)
newline
s(t) = sum from {k in K} {A_k cdot cos left(2 cdot %pi cdot f_k cdot t + %phi_k right)}
newline
s_1(t) = cos left(2 cdot %pi cdot 500 cdot t - {%pi} over {2} right)
newline
s_2(t) = cos left(2 cdot %pi cdot 1000000 cdot t right) + 0,25 cdot cos left(2 cdot %pi cdot 990000 cdot t + {%pi} over {2} right) + 0,25 cdot cos left(2 cdot %pi cdot 1010000 cdot t - {%pi} over {2} right)