What did I do wrong in calculating this derivative?

[itsrayex]

I'm trying to solve this:

which yelds this result:


But this is what I got:

I don't understand why there is still a -5 in the given solution. Can someone please help me?

Thank you

 

[lev888]

I'm trying to solve this:
View attachment 30918
which yelds this result:

View attachment 30919
But this is what I got:
View attachment 30920
I don't understand why there is still a -5 in the given solution. Can someone please help me?

Thank you

You lost it on the second line.

 

[BigBeachBanana]

You didn't FOIL correctly here. Try again.