9) Find all critical numbers of the function

Question

f(t)=9t^2/3+t^5/3

Answer 1

f(t) = 1/3 (9t^2 + t^5)
f'(t) = 1/3 (18t + 5t^4)
= 1/3 t(18+5t^4)

f'=0 where x=0 or ±∜3.6