Math 215 - Multivariate Calculus - Schedule

Rapid Recall

A rover moves in a straight line to a new spot that is 2 m east and 3 m south of its current location. The rover's height rises 2 m along the way. What the slope of the hill in the direction the rover moved?
A rover is located on a hill whose elevation is given by $z=f(x,y) = xe^{3xy}$. Compute the differential $dz$ and write it in the form $dz=(?)dx+(?)dy.$ In your solution, circle $f_y$ an put a box around $\ds\frac{\partial f}{\partial x}$.
A right cylindrical rod, with radius $r$ and height $h$, has volume given by $V=\pi r^2 h$. If we increase $r$ by $dr$, and increase $h$ by $dh$, then use differentials to estimate the increase in volume. (I'll draw a picture on the chalkboard that visually shows the answer.)

A rover is located on a hill whose elevation is given by $z=f(x,y) = 3xy+y^2$.
- Compute the differential $dz$, and write it in the form $dz=(?)dx+(?)dy.$
- State $\dfrac{\partial f}{\partial x}$ and $f_y$. Then give $\vec \nabla f$.
- State the differential at the point $P=(1,1)$ (the spot where the rover currently resides).
- What is the slope of the hill at $P=(x,y)=(1,1)$ in the direction $(dx,dy)=(1,0)$?
- What is the slope of the hill at $P=(1,1)$ in the direction $(0,1)$?
- What is the slope of the hill at $P=(1,1)$ in the direction $(3,4)$?
The sides of a rectangle $x=3$ ft and $y=2$ ft, with tolerances $dx = .1$ ft and $dy = 0.05$ ft. Use differentials to estimate the tolerance on the area $A=xy$ that results from the given tolerances on $x$ and $y$.
Let $g(x,y) =x^2y$.
- Give $g_x$ and $\dfrac{\partial g}{\partial y}$. Then state $\vec \nabla g$.
- Find the directional derivative (slope) of $g$ at $P=(3,1)$ in the direction $(-3,2)$.
- Find the directional derivative of $g$ at $P=(3,1)$ in the direction $(2,-5)$.
The sides of a box are supposed to be $x=3$ ft by $y=2$ ft by $z=1$ ft, with tolerances $dx = .1$ ft by $dy = 0.05$ft by $dz=0.02$ft. Use differentials to estimate the tolerance on surface area $A=2xy+2yz+2xz$ that results from the given tolerances.