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a)sin(2(pi)t)+cos(13(pi)t-pi/4)

b)sin(3t)-cos[(pi)t]

I know to find the period of the combined motion you do T=n

_{1}T

_{1}=n

_{2}T

_{2}where the n's are integers, so I believe the frequency of the combined motion is just the inverse of the combined period.

For a), I found the period of the sine function to be 1/6, and the period of the cosine function to be 2/13, so T=12(1/6)=13(2/13)=2s, so the frequency is 1/2 Hz...but the answer is actually 6.25 hz.

For b) I found the period of the sin function to be (2/3)pi, and that of the cosine function to be 2, so n

_{1}(2/3)pi=n

_{2}2 has no integer solutions, so there is no determined combined period and thus no determined combined frequency either...but the answer is 0.49 Hz...

Can someone help me please? I already successfully did one of them, but I can't get these..

Also, does it make a difference whether the functions are being added or subtracted?