Objectives
This unit covers the following ideas.
- Explain the properties of the gradient, its relation to level curves and level surfaces, and how it can be used to find directional derivatives. 
- Find equations of tangent planes using the gradient and level surfaces. Use the derivative (tangent planes) to approximate functions, and use this in real world application problems. 
- Explain the second derivative test in terms of eigenvalues. Use the second derivative test to optimize functions of several variables. 
- Use Lagrange multipliers to optimize a function subject to constraints.