Second derivative test vs Lagrange multipliers

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Hi I just have a quick question about optimization for multi-variable functions. I know you can optimize using the second derivative test for a bounded region on the graph, but I don't know how the methods as described in this video (https://www.youtube.com/watch?v=wkQp2ifFHP8&t=906s) are different than using Lagrange multipliers. To me they both optimize with a constraint.