Valhalla Legends Archive

Member Forums => Yoni's Math Forum => Topic started by: Raven on June 06, 2004, 11:07 AM

Title: Another riddle!
Post by: Raven on June 06, 2004, 11:07 AM
A rectangle has one side on the positive x-axis, one side on the positive y-axis, and its upper right-hand vertex on the curve y = e^-4x. What dimensions (LxH) give the rectangle its largest area and what is that area? :)
Title: Re:Another riddle!
Post by: Yoni on June 06, 2004, 11:46 AM
1/4 x 1/e with an area of 1/4e. Looks more like a calculus 1 homework problem than a cool riddle... :(
Title: Re:Another riddle!
Post by: K on June 06, 2004, 11:47 AM
I might have made a mistake somewhere, but I got:
width = 1/4 => height = 1/e

width = x;
height = e-4x
area = x*e-4x

dA/dx = -4x*e-4x + e-4x = e-4x(-4x + 1)

e-4x(-4x + 1) = 0
(-4x + 1) = 0; e-4x != 0;
-4x = -1
x = 1/4
Title: Re:Another riddle!
Post by: K on June 06, 2004, 11:48 AM
Quote from: Yoni on June 06, 2004, 11:46 AM
1/4 x 1/e with an area of 1/4e. Looks more like a calculus 1 homework problem than a cool riddle... :(

way to reply while i was trying to find a calculator to graph it to check my answer.
Title: Re:Another riddle!
Post by: Raven on June 06, 2004, 03:52 PM
Quote from: Yoni on June 06, 2004, 11:46 AM
1/4 x 1/e with an area of 1/4e. Looks more like a calculus 1 homework problem than a cool riddle... :(

Yup, that it is, but I thought you may still get atleast a kick out of it. :)
Title: Re:Another riddle!
Post by: Yoni on June 07, 2004, 03:20 AM
Not cool enough to be kickworthy imo.