The two graphs show quantities directly proportional in the first graph and inversely proportional in the second graph.
For the first graph we can write down,
and for the second graph
where, in each case,is a constant of proportionality.
We are typically asked something like:
The amount of petrolused by a car is directly proportional to the distance travelled,
Example: The intensity of lightfrom a bulb is inversely proportional to the distance
a)Write down an expression relatingand
Ifwhen, find an equation betweenand
b)Use your equation to findwhen
c)Use you equation to findwhen