Functions of two (or more) variables [9.1]

Example: Covid risk chart

Texas Medical Center, continuing updates
$$R(a,v,f,c,o)$$

Risk, $R$ (as indicated by colors) is a function of five variables:
$a$ is the level of verbal activity,
$v$ is the degree of ventilation in the space you're in,
$f$ is the effectiveness of your face covering,
$c$ is the contact time of the activity.
$o$, occupancy a relative measure of how many people (and how tightly packed) in a space.

Edfinity, problem #2

The tricky thing here is that you need to enter the variable name in the first column. So, in the correct (but partial) version of the problem below, the actual temperature, $T$ is the "independent variable":

Edfinity, problem #4

The diagram in problem 4 contains information about the revenue, $R(c,d)$ (in dollars) of a (late 90s) music store, which depends on $c$, the number of CDs sold, and $d$, the number of DVDs sold.

The green point shown has coordinates $(c,d)=(50,250)$ and lies on the blue line for $R$=\$4000. This means:

When the store sells 50 CDs, and 250 DVDs, its revenue is $R$=\$4000.

The numbers underlined in red refer to the revenue of any $(c,d)$ point on one of the dark blue lines.