
Bradford T. answered 05/28/21
Retired Engineer / Upper level math instructor
Let L = lim h→0
f(t) = t4/2 -5t-3
f'(t) = L ((t+h)4/2-5(t+h)-3 - t4/2+5t+3)/h
= L ((t4+4t3h+6t2h2+4th3+h4)/2 -5t-5h-3 -t4/2+5t+3)/h
= L ((4t3h+6t2h2+4th3+h4)/2-5h)/h
= L (4t3+6t2h+4th2+h3)/2 -5
= 4t3/2 - 5
= 2t3-5