Question

Calculus help please! Fist time taking this class

The number of flowers planted, t hours after starting at 8, is given N(t)=18t_6t^2-1.3t^3
A) how many flowers had been planted by 11am?
B At what rate is the number of flowers planted changing at 11am?

Answer 1

I am assuming 8am.

11 is 3 hours after 8 so we want to let t = 3.

For A you substitute 3 into the original equation
The B you substitute 3 into the derivative (or find a limit) or use any other method for finding instantaneous ROC.

Answer 2

Does that help you? Or can you not find the instantaneous ROC

Answer 3

yes thank you! if i need more help is it okay if i message you?

Answer 4

If i'm still online then sure

Answer 5

Can i get some help with part b?

Answer 6

@Riddellikins

Answer 7

What part do you need help with? Or where are you up to?

Answer 8

deriving the equation

Answer 9

for part b

Answer 10

N(t)=18t_6t^2-1.3t^3

Answer 11

Equation and draw buttons are not working for me for some reason. I will do it now :P

Answer 12

Is that underscore between 18t and 6t^2 meant to be a subtract?

Answer 13

sorry i made a mistake there the equation is 18t+6t^2-1.3t^3

Answer 14

Okay, I can do it now :)

Answer 15

is the derivative t=4.35897+3.07692 t?

Answer 16

N(t) = 18t+6t^2-1.3t^3

I derive using differentiation (I think)
To do this you multiply the exponent (of the variable, t in this case) by the coefficient for each term and then you decrease the exponent by 1.

N'(t) = 18x1 t^(1-1) + 6x2 t^(2-1) - 1.3x3 t^(3-1)
N'(t) = 18t^0 + 12t - 3.9t^2
N'(t) = 18 + 12t - 3.9t^2

Answer 17

If you need help deriving then wolfram alpha is a great tool to check your answers:

http://www.wolframalpha.com/input/?i=derivative+18t%2B6t%5E2-1.3t%5E3

Answer 18

Omg your the best thank you for all your help!