I'm stuck on this one:
f(x)=5t−9t2
f′(x)=limh→05(h+a)−9(h+a)2−5a−9a2h
f′(x)=limh→05(h+a)−9(h2+2ha+a2)−5a−9a2h
f′(x)=limh→05h−9h2−18ha−18a2h
I don't know where to go from here...