Is the equation #y=3-x# a direct variation, if so what is the constant of variation?

1 Answer
Oct 23, 2015

#y=3-x# is not a direct variation

Explanation:

If #y=f(x)# is a direct variation
then for all values #(x,y)# satisfying #y=f(x)#
#color(white)("XXX")y/x = c# for some constant #c#

Checking a few sample solutions:
#{: (x,color(white)("XX"),y,color(white)("XX"),y/x), (1,color(white)("XX"),2,color(white)("XX"),2), (2,color(white)("XX"),1,color(white)("XX"),1/2), (3,color(white)("XX"),0,color(white)("XX"),0) :}#

Obviously the ratio #y/x# is not a constant for this example
and therefore this is not a direct variation.