Hello,
which principle?
f(x)=-x²+2x
==>f'(x)= -2x+2
You mean maybe this

f(x+h)=-(x+h)²+2(x+h)= -(x²+2hx+h²)+2x+2h
f(x)=-x²+2x
Answer:
The possible ways Daniel line up his rock collection are {2, 3, 6 and 9}.
How long is the trail on your table then multiply by 6.
So, difference as in subtract? so, if it is, it would be 15. if it means percent difference, it's about 60%.