We have the following statement: "A varies jointly as both b and h."
We have to find a mathematical model for this statement.
When a variable varies jointly as other variables, it means it has a proportional relationship to them.
In this case, we have a variable A, which caries jointly with b and h, so we can write a general model as:
where k is the constant of proportionality and it can take any non-zero value.
For example, if k=2, we have:
Then, for any change in b or h (or both together), we have a proportional variation in A.
Answer:
The general model is A = k*b*h.