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Math 1310-online
Test-2 OCT 13 and Oct 14 make reservation in CASA
PT-2 due OCT 14
Quiz 6 due Oct 19
HW:12 due 10-11
Section 3.3
Direct Variation:
If a situation is described by an equation in the form
y = kx
where
k
is a nonzero constant, we say that
y
varies directly as
x
or
y
is directly
proportional to
x
.
The number
k
is called the
constant of variation
or the
constant of proportionality
.
Example:
Sales Tax varies directly as the sale price of an item.
The larger the sale, the more tax to be paid.
The smaller the sale, the less tax to be paid.
Other ways to say direct variation:
y varies directly as x.
y varies with x.
y is directly proportional to x.
y is proportional to x.
Inverse Variation:
If a situation is described by an equation in the form
y = k/x
where
k
is
a nonzero constant, we say that
y
varies inversely as
x
or
y
is inversely
proportional to
x
.
The number
k
is called the
constant of variation
or the
constant of proportionality
.

Example:
In the formula, T = D/R, time varies inversely as the rate,
given that D is a constant.
The faster you go, less time it takes to get there.
The slower you go, the more time it takes to get there.
Joint Variation:
If a situation is described by an equation in the form
y = kxy
where
k
is a nonzero constant, we say that
y
varies jointly as
x
and
y
.
The number
k
is called the

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