Two quantities (x,y) are proportional if one is a constant (k) multiple of the other (y=kx for some constant k.) Two quantities (x,y) are jointly proportional to a third quantity (z) if their product is a constant multiple (k) of the third (z=kxy).
1. Write differential equations for the following scenarios:
a. The rate of infection is constant.
b. The rate of infection is increasing at a rate that is proportional to the number of infected people.
c. The rate of infection is increasing at a rate that is proportional to the number of infected people and decreasing at a rate that is proportional to the number of infected people.
d. The rate of infection is increasing at a rate that is jointly proportional to the number of infected people and the number of healthy people.
e. The rate of infection is increasing at a rate that is jointly proportional to the number of infected people and the number of healthy people and decreasing at a rate that is proportional to the number of infected people.