The distance, d, in kilometres, travelled by a plane after t hours can be represented by d(t)=-4t^3=40t^2+500t, Where t is greater than or equal to 0 and less than or equal to 10. How long does the plane take to fly 4088km?

Question

phi · Answer

is there a typo in your equation?

anonymous · Answer

yes, d(t)=-4t^3+40t^2+500t

phi · Answer

they want you to solve for "t"  when
$$ -4t^3+40t^2+500t=4088 $$
or
$$ -4t^3+40t^2+500t-4088=0 $$

phi · Answer

we can simplify that equation a little by dividing both sides by -4
$$ t^3 -10t^2 -125t +1022 = 0 $$

anonymous · Answer

and then what

phi · Answer

we can graph it

phi · Answer

What are you studying?

anonymous · Answer

Advanced functions and solving polynomials

phi · Answer

This is a cubic, and though cubics have a "closed formula", it is a bit hairy.
Are you supposed to use that formula?  i.e. how do they expect you to solve this?

anonymous · Answer

i have no idea ! lol

phi · Answer

Are you saying you never saw an example of solving a cubic?

anonymous · Answer

we are taught to factor it and find the zeros