CALCULUS PROBLEM

Discus: SAT/ACT Tests and Test Preparation: CALCULUS PROBLEM
 By Aznhermit (Aznhermit) on Tuesday, October 05, 2004 - 02:01 am: Edit

I have a test tomorrow and if someone can help that would be GREAT!!!

A rectangluar field is to be enclosed with 240m of fence. a) find mathematical Model espressing the area of the field as a funciton of its length. b) what is the domain of your funciton in part (a) and part (c) i get... so its ok

I got the right answer for part (a)... but the part (b) its really wierd... i tried to find where its 0 so it cant be negative so i got [0,120] ... but then when my teacher explained it (not all the great of a teacher) he said that it was [60,120]. But i thought i was doing it right... am i right or is he wrong...

 By Imblue (Imblue) on Tuesday, October 05, 2004 - 03:02 am: Edit

It's just a technicality regarding the definition of length, which is the longer side of a rectangle. The length cannot be less than 60, since that would mean the width is longer.

 By Cognitio (Cognitio) on Saturday, October 09, 2004 - 06:30 pm: Edit

P = 2L + 2W
implies W = (P - 2L)/2
so A = LW = L(P - 2L)/2
and A = (PL)/2 - L^2
thus A(L) = -(L^2) + 120L

Something like that

 By Cognitio (Cognitio) on Saturday, October 09, 2004 - 06:31 pm: Edit

Not a calculus problem by the way

 By Lolboyer (Lolboyer) on Monday, October 11, 2004 - 06:58 pm: Edit

since for some reason i cannot create new threads ill post this here
if a question asks you to see if the velocity of something in increasing and you're given the displacement function, you would have to graph the velocity function. from there would u need to graph the acceleration function... because from the velocity function isnt it obvious where the speed in increasing. like if the velocity function is y=x^2, wouldnt the speed be increasing from 0 to infinity? help pls.. thanks