Ok so it actually goes with chain rule.

What is chain rule? See dy/dx which explains you rate of change of Y with respect to X can also be written as product of two different rates dy/dt and
dt/dx.

First term gives you rate of change of Y with respect to t and second rate of change of t with respect to x, see class, this can also be written as dy/dt
multiplied by dt/dp multiplied by dp/dq and multiplied by dq/dx. You can form a chain even an infinitely long chain so that is why it is known as Chain
Rule.

For given differential dy/dx can be considered as product of two or minimum two separate differentials.

This particular approach will allow you to solve some good problems of differentials done.

Say if Y = sin (x ^2). Find dy/dx.

Now see this Y = sin (x^2)

This is not our standard formula. What is our standard formula? sine X, sine θ, sine of anything power 1 so you cannot say the differential will be
directly because differential of sin X is cos X so this will be cos (x^2) that is not correct. That means the rules or the list of formulae that we have
prepared is would not be applicable here directly because function is not falling in to required format. So what is required format? If it was sin X then
our problem would have been easy it would have been cos x of sin x. Then what to do? What will be our planning? Now listen carefully.