This could also be written as

`del/(dely)[(delF)/(delx)]`

This expression means:

"First, find the partial derivative with respect to x of the function F (this is in brackets), then find the partial derivative with respect to y of the result ".

In our example above, we found

`(delF)/(delx)=6\ cos\ x`

To find `(del^2F)/(delydelx)`, we need to find the partial derivative with respect to y of `(delF)/(delx)`.

` (del^2F)/(delydelx)=del/(dely)[(delF)/(delx)] `

`=del/(dely)[6\ cos\ x]`

`=0`

Since cos x is a constant (when we are considering differentiation with respect to y), its derivative is just 0.


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