How to use function spectrum in R to perform spectral analysis
Hi: Your sampling frequency is $f_{s} = 10 $ but the frequency of the third component is $f_{3} = 6$.. Therefore, the nyquist criterion for  the maximum frequency is not being met because $2 * 6 = 12$ which is not less than $f_{s} = 10$. I'm new at this but hopefully this is the reason why. Someone will surely correct me if not.