# Amplitude modulation in pure sine wave [duplicate]

I am generating sine wave in MATLAB with following code

fs=2000e6;%sampling frequency
t=0:1/fs:(1e-6)-1/fs; %1us seconds duration
fc=501e6;%frequency of the cosine wave
x=cos(2*pi*fc*t);
plot(x)


The wave it generates is somehing like this

My question is: Why do we see amplitude modulation in the wave. Shouldn't amplitudes be 1 at all peaks of the wave? like this wave