A particle executes SHM with angular frequency 6.28 s-1 and amplitude 10 cm .what will be the speed at t=1/6 s assuming that the motion starts from rest at t = 0 . The solution is given as in the picture .The displacement equation has cos instead of sin and so does the equation of velocity has sin instead of cos ... why..?!! Does it change like this if yes then what should be kept in mind while solving such numericals..??! Kindly explain properly it's really important

A particle executes SHM with angular frequency 6.28 s-1 and amplitude 10 cm .what will be the speed at t=1/6 s assuming that the motion starts from rest at t = 0 . The solution is given as in the picture .The displacement equation has cos instead of sin and so does the equation of velocity has sin instead of cos ... why..?!! Does it change like this if yes then what should be kept in mind while solving such numericals..??! Kindly explain properly it's really important may be written as A covet is v • — A Sin