Question 652069
This is how you write a direct proportion. The symbol in the middle is the Greek letter alpha.

{{{x (alpha)y}}}


It reads: {{{x}}} is directly proportional to {{{y}}}.


It means: By whatever factor {{{x }}}changes, {{{y}}} changes by the same factor.

Here is an example of a point you can put on a graph. The point is ({{{x1}}}, {{{y1}}}) and it has coordinates ({{{1}}}, {{{1}}}). 

Coordinates for second point ({{{x2}}}, {{{y2}}}) are ({{{3}}}, {{{3}}})

as we can see, {{{x}}}  changes by a factor of {{{3}}}. That is, {{{x1}}} times a factor of {{{3}}} equals {{{x2}}}, and

as we can see, {{{y}}}  changes by a factor of {{{3}}}. That is, {{{y1}}} times a factor of {{{3}}} equals {{{y2}}}

Therefore, {{{x}}} is directly proportional to {{{y}}}, {{{x (alpha)y}}}.


Also, {{{x}}} could be {{{inversely}}} proportional to {{{y}}}. It means: By whatever factor {{{x}}} changes, {{{y}}} changes by the {{{inverse}}} of that factor. (Or you could say, “by the reciprocal of that factor”.)

in example above {{{x}}} changes by factor {{{3}}}; so, {{{y}}} changes by the {{{inverse}}} of that factor which is {{{1/3}}}.