1. Ch. 9.1 Inverse Variation

2. y = x and y vary inversely.
Inverse Variation
ALGEBRA 2 LESSON 9-1
Suppose that x and y vary inversely, and x = 7 when y = 4. Write the function that models the inverse variation.
y = x and y vary inversely. k x
4 = Substitute the given values of x and y. k 7
28 = k Find k.
y = Use the value of k to write the function. 28 x
9-1

3. Check understanding #1 p. 479

4. The product of each pair of x- and y-values is 1.4.
Inverse Variation
ALGEBRA 2 LESSON 9-1
Is the relationship between the variables in the table a direct variation, an inverse variation, or neither? Write functions to model the direct and inverse variations. x y a.
The product of each pair
of x- and y-values is 1.4.
As x increases, y decreases.
y varies inversely with x and
the constant of variation is 1.4.
So xy = 1.4 and the
function is y = .
1.4 x
x –2 –1.3 7
y 6 5 –4 b.
As x increases, y decreases, but this is not an inverse
variation.
Not all the products of x and y are the
same (–2 • –1.3 • 5). = /
This is neither a direct variation
nor an inverse variation.
x –2 4 6
y 5 –10 –15 c.
As x increases, y decreases.
Since each y-value is
–2.5 times the corresponding x-value, y varies directly with x and the constant of variation is –2.5, and the function is y = –2.5x.
9-1

5. Check understanding #2 A – C p. 479

6. Homework
Page 481, Exercises: 2 – 14 e,