Which of the following expression does not represent SHM?
A cos ωt
A sin 2 ωt
A sin ωt + B cos ωt
A sin2 ωt
For SHM, d2ydt2 ∝ -y
If y = A sin2 ωt
dydt = (2A sin ωt cos ωt)ω
= = Aω sin 2 ωt
d2ydt2 = +2 Aω2cos 2 ωt
i.e., d2ydt2 is not proportional to -y