This could also be written as

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

This expression means:

"First, find the partial derivative with respect to

xof the functionF(this is in brackets), then find the partial derivative with respect toyof 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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