## Direct and Inverse Proportion

Direct Proportion

If two quantities and are in direct proportion then they increase together by the same ratio. If one doubles so does the other, and if one increases by a factor of 10, so does the other. We can write down the relationship between these two quantities in the form of an equation, where is the constant of proportionality. We may have to find but once we have found it, then we can find for any given value of or for any given value of  Direct proportion is illustrated on the graph above. For this direct proportion relation the gradient of the graph. We can also find if we are told specific values of and If we are told that when then Now we know that we can:

Find if Find if Inverse Proportion

Two quantities and are inversely proportional if their product is a constant – we can also write this equation as The graph of two quantities in inverse proportion is given below. We can find k if we are told specific values of and If we are told that when then Now we know that we can:

Find if Find if  