how do i tell when what answers our direct variation between x and y when solved for y

Question

a. y-9=2x+9     b. y=4/7x   c. 4+y=1/3x+4    D.y=3/x            When i put 4/7 or 1/3  its over- i don't know how to enter it right

Answer 1

a) y=2x+18, direct variation

b) y=(4/7)x, direct variation

c) y=(1/3)x, direct variation

d) y=3/x, indirect variation because as x gets larger, the fraction 3/x gets smaller (3/x=y)

if x=4, y=3/4 or 0.75, if x=8, y=3/8 or 0.375, x=10, y=0.3, x=100, y=0.03

Answer 2

Direct variation means that when one variable increases in value, the other variable will also increase in value. On the other hand, one variable decreases in value, the other will decrease. This relationship is best represented by the following generic formula:

 

y = kx

 

 

Indirect variation means that when one variable increases in value, the other variable will decrease in value. On the other hand, one variable decreases in value, the other will increase. This relationship is best represented by the following generic formula:

 

y = k/x

 

Based on the above information, the best answer would be (a).