Two quanties may have a range of relationships. Usually the best way to establish a relatioship is to plot a graph of one quantity against the other. Possible relationships between two quantities are shown below.
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x and y are directly proportional. We can write y=kx where k is a constant of proportionality. |
There is a linear relationship between x and y. We can write y=mx+c |
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x and y increase together but are not linearly related. |
If x increases y decreases and vice versa. There is no linear relationship between x and y. |
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There is a negative linear relationship between x and y. We can write y=mx+c where m is negative. |
There is a negative relationship between x and y but the relationship is not linear. If x increases, y decreases and vice versa. |
