1. A rover travels along the line $2x+3y=6$. The surrounding terrain has elevation $z=x^2+4y$. The rover reaches a local minimum along this path.
    • State the function $f$ to optimize, and the constraint $g=c$.
    • Compute $\vec \nabla f$ and $\vec \nabla g$.
    • Write the system of equations that results from $\vec \nabla f=\lambda\vec \nabla g$ together with $g(x,y) = 6$.
    • Solve the system above (you should get $x=4/3$ and $y=10/9$).
  2. Consider the function $f(x,y)= 2x^2+3xy+4y^2-5x+2y$.
    • Find all critical points of $f$.
    • Determine the eigenvalues of the second derivative at each critical point. Do we have a max, min, or saddle?
  3. Consider the function $f(x,y,z) = 3xy+z^2$. We'll be analyzing the surface at the point $P=(1,-3,2)$.
    • If $dx=0.1$, $dy=0.2$ and $dz=0.3$, then what is $df$ at $P$.
    • Give an equation of the tangent plane to the level surface of $f$ that passes through $(1,2,-3)$.
    • Give an equation of the tangent plane to the level surface of $f$ that passes through $(a,b,c)$.
  4. Give an equation of the tangent plane to $xy+z^2=7$ at the point $P=(-3,-2,1)$.
  5. Give an equation of the tangent plane to $z=f(x,y)=xy^2$ at the point $P=(4,-1,f(4,-1))$.
    • Find the directional derivative of $f(x,y)=xy^2$ at $P=(4,-1)$ in the direction $(-3,4)$.

Problem Set
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