1)Use Lagrange multipliers to find shortest distance from (10,-4,9) to the plane 7x+8y-10z=4
- I tried to use d=sqrt((x-10)^2+(y+4)^2+(z-9)^2) then split each one up to 2(x-10)=7h , 2(y+4)=8h , 2(z-9)=-10h
- I then solved for x,y,z and plugged into the original equation of 7x+8y-10z=4 got I got h=112/213 which is not correct and I'm not sure where I messed up.
2)Use lagrange multipliers to find volume of largest rectangular box in first octant with 3 faces in coordinate planes and one vertex in plane x+5y+2z=30.
-I use V=xyz and got yz=h , xz=5h , xy=2h , x+5y+2z=30
- Not sure where to go after this.
Feb 16th 2008, 06:05 PM
For the first one, you can easily check your answer by using the distance from a point to a plane formula. But first....the long way.
Subject to the constraint
Which leads to the equation:
So, we have:
From the first two equations we get:
From the first and third we get:
Sub these into the constraint and get:
Solving for x we get
Which leads to
Sub these into g(x,y,z):
Check it with the distance formula:
Feb 16th 2008, 06:34 PM
worked out perfectly. When I plugged x,y,z into distance I got (56*sqrt(213)) / 213. Thanks for the steps that helped me a lot.