first it is mentioned that 'dy' should not be considered as "d" multiplied with y,but for the second order derivation for the formula of acceleration, they have considered "d"multiplied with "y".Why it is so??

first it is mentioned that 'dy' should not be considered as "d" multip

1.	first it is mentioned that 'dy' should not be considered as "d" multiplied with y,but for the second order derivation for the formula of acceleration, they have considered "d"multiplied with "y".Why it is so??
Answer» first it is mentioned that 'dy' should not be considered as "d" multiplied with y,but for the second order derivation for the formula of acceleration, they have considered "d"multiplied with "y".Why it is so??