Download Write and graph a direct variation equation EXAMPLE 1

EXAMPLE 1
Write and graph a direct variation equation
Write and graph a direct variation equation that has
(– 4, 8) as a solution.
SOLUTION
Use the given values of x and y to find the constant of
variation.
y = ax
Write direct variation equation.
8 = a(– 4)
Substitute 8 for y and – 4 for x.
–2= a
Solve for a.
EXAMPLE 1
Write and graph a direct variation equation
ANSWER
Substituting – 2 for a in y = ax gives the direct variation
equation y = – 2x. Its graph is shown.
GUIDED PRACTICE
for Example 1
Write and graph a direct variation equation that has the
given ordered pair as a solution.
1.
(3, – 9)
SOLUTION
Use the given values of x and y to find the constant of
variation.
y = ax
Write direct variation equation.
–9 = a(3)
Substitute – 9 for y and 3 for x.
–3= a
Solve for a.
GUIDED PRACTICE
for Example 1
ANSWER
Substituting – 3 for a in y = ax gives the direct variation
equation y = – 3x. Its graph is shown.
GUIDED PRACTICE
for Example 1
Write and graph a direct variation equation that has the
given ordered pair as a solution.
2.
(– 7, 4)
SOLUTION
Use the given values of x and y to find the constant of
variation.
y = ax
4 = a(– 7)
–4 =a
7
Write direct variation equation.
Substitute 4 for y and – 7 for x.
Solve for a.
GUIDED PRACTICE
for Example 1
ANSWER
–4
Substituting 7 for a in y = ax gives the direct variation
equation y = – 4 x. Its graph is shown.
7
GUIDED PRACTICE
for Example 1
Write and graph a direct variation equation that has the
given ordered pair as a solution.
3.
(5, 3)
SOLUTION
Use the given values of x and y to find the constant of
variation.
y = ax
Write direct variation equation.
3 = a(5)
3 =a
5
Substitute 3 for y and 5 for x.
Solve for a.
GUIDED PRACTICE
for Example 1
ANSWER
Substituting 3 for a in y = ax gives the direct variation
5
equation y = 3 x. Its graph is shown.
5
GUIDED PRACTICE
for Example 1
Write and graph a direct variation equation that has the
given ordered pair as a solution.
4.
(6, – 2)
SOLUTION
Use the given values of x and y to find the constant of
variation.
y = ax
Write direct variation equation.
– 2 = a(6)
–1 =a
3
Substitute – 2 for y and 6 for x.
Solve for a.
GUIDED PRACTICE
for Example 1
ANSWER
Substituting– 1 for a in y = ax gives the direct variation
3
equation y = – 1 x. Its graph is shown.
3