Hello, crystal91!
This is a killer!
Note that: .Differentiate using first principles.
We will differentiate . . . and multiply by at the very end.
[1] Find
. . . . . a difference of cubes
. . Factor:. . .
. . Multiply by
. . and we have: .
[2] Divide by
[3] Take the limit: .
. . . . . . . . . . . .
Multiply by