So this is our table:
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x-values | a b c d e f |
-----------------
y-values | g h i j k l |
-----------------
You can know that the values in the table are proportional if:
[tex]\frac{a}{g}=\frac{b}{h} =\frac{c}{i}=\frac{d}{j}=\frac{e}{k}=\frac{f}{l}[/tex]
Hope that helps :)