plot fourier transform

[aidana]

i have this equation with 4 frequencies as 5,10,520,50 : x=cos(2*pi*5*t)+ cos(2*pi*10*t)+ cos(2*pi*20*t)+ cos(2*pi*50*t), i want plot this,but i don't know,which zone i should use, to see all 4 frequencies and how can i plot this in an appropriate time zone?
using try and error method i find that t=(0:.001:1) is appropriate... then using fft(x) i found the fourier transform of it,now i want plot the fft but i cant,plz help me.....

 

[_Eduardo_]

5 periods are 1", but to evaluate the fft from samples of 0.001" , the interval must be t=(0:0.001:0.999)

Or better, use 1 period range --> t = (0:0.001:0.199);

t=(0:.001:.199) ; x=cos(2*pi*5*t)+cos(2*pi*10*t)+cos(2*pi*20*t)+cos(2*pi*50*t) ; y=fft(x) ; plot(real,'.')