The correct option is C 3
Given
y=4cos2(t2)sin(1000t)
Using 2cos2θ=1+cos2θ, we get
y=2×2cos2(t2)sin(1000t)
y=2×(1+cost)sin(1000t)
y=2sin(1000t)+2sin(1000t)cost
y=2sin(1000t)+sin(1000t+t)+sin(1000t−t)
[Using 2sinAcosB=sin(A+B)+sin(A−B)]
y=2sin(1000t)+sin(1001t)+sin999t
y=sin(1000t)+sin(1000t)+sin(1001t)+sin(999t)
Thus, the given expression is composed of four SHMs, out of which two are the same. This means that the given expression is the result of 3 independent harmonics.