Section 98
Direct and Inverse Variation
Direct variation
describes a simple relationship between two variables. We say
y
varies directly
with
x
(or
as x
, in some textbooks) if:
y
=
k
x
for some constant
k
.
The graph of the direct variation equation is a straight line through the origin.

Direct Variation Equation
for 3 different values of
k

Inverse variation
describes another kind of relationship. We say
y
varies inversely
with
x
(or
as x
, in some textbooks) if
:
xy
=
k
,
or, equivalently,
for some constant
k
.
The graph of the inverse variation equation is a hyperbola.

Inverse Variation Equation
for 3 different values of
k
