clear
clc

A = 10;
A2 = 5;
f = 2;
f2 = 3;
t = 0:0.01:30;
fp = 100;

%dt = (t(2)-t(1))
df = 1/ max(t);
ff = 0:df:max(t)*df;

nr = f/df;

x = A * sin(2*pi*f*t) + A2 * sin(2*pi*f2*t);

plot(t, x);
pause

X = abs(fft(x));

freq=(0:1:4*nr)*df;

X = X/(length(X)/2);

plot(freq, X(1:length(freq)));