Direct and Inverse Proportion
The two graphs showquantities directly proportional in the first graph and inverselyproportional in the second graph.
For the first graph we canwrite down,
and for the second graph
where, in each case,isa constant of proportionality.
We are typically askedsomething like:
The amount of petrolusedby a car is directly proportional to the distance travelled,
Example: The intensity oflightfroma bulb is inversely proportional to the distance
a)Write down an expressionrelatingand
Ifwhen,find an equation betweenand
b)Use your equation tofindwhen
c)Use you equation tofindwhen