- #1
Panphobia
- 435
- 13
Homework Statement
Find the dimensions of the rectangle of greatest and least area
that can be inscribed in the ellipse x^2/16 + y^2/9 = 1 with sides parallel
to the coordinate axes.
The Attempt at a Solution
f(x,y) = (2x)(2y) = 4xy
∇f = <4y,4x>
∇g = <x/8,2y/9>
∇f = λ∇g
4y = λx/8
4x = λ2y/9
I can isolate lambda because y=0,x=0 is not a part of the ellipse.
λ = 32y/x
λ = 18x/y
32y/x = 18x/y
x^2 = 16y^2/9
Sub into ellipse
2y^2/9= 1
y = 3/√2
x = 2√2
I don't know what to do after this, I know I am supposed to check whether it is a maximum or not, but I don't know the method. What would the next step be?