Lagrange functions

[joshmeyer]

I don't really understand how to approach problems that require me to solve using lambda.
I understand the generalities of what the purpose of the function is, but not how to get there. I've been reading through my text and I watched this youtube clip

, but I'm still having trouble grasping it.

 

[Steven G]

Can you show your attempt or at least state which step you are having trouble with?

 

[joshmeyer]

Can you show your attempt or at least state which step you are having trouble with?

I hit a breakthrough and made it further. I just now don't understand where to plug in the coordinates to find the minimum

 

[Steven G]

I just now don't understand where to plug in the coordinates to find the minimum

Which function are you trying to find the extremum of? Plug the values into that function.
Does (0,4) satisfy the constraint? What is the value of f(0,4)? Does this value tell you something?

 

[joshmeyer]

Which function are you trying to find the extremum of? Plug the values into that function.
Does (0,4) satisfy the constraint? What is the value of f(0,4)? Does this value tell you something?

0,4 does fit within the constraints of the function, and has a lower value (0). Are legrange functions entirely different from the previous work I've been doing with partial derivatives? Where I was finding relative maximums/minimums, which was easily distinguished by the signage of the x/y with the highest powers. Here it is almost the maximum possible value in order to make 7x+y=4 true?