helicopter moves vertically. Height above start point = y height at t seconds = y= (1/4)t^4 -26t^2 + 96t t = between 0 and 4 differentiate to find velocity = t^3 + 52t + 96 acceleration = 3t^2-52 thats part 1 of question done, easy. Verify that y has a stationary value when t = 2 determine whether it is min/max value. i can put this into 3t^2-52t+96 and find out that it is. but how is it min/max nevermind : i put it into acceleration and find out if acceleration is more or less than the value i got for velocity. If it's less i know that the thing will never accelerate again after this given time. so it would be a maximum. Where as if it was more than the value i got for velocity i know that the object would be able to accelerate again, which is minimum.. right?