EXAMPLE 1 Write and graph a direct variation

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EXAMPLE 1 Write and graph a direct variation equation that has (– 4, 8)

EXAMPLE 1 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

EXAMPLE 1 Write and graph a direct variation equation ANSWER Substituting – 2 for a in y = ax gives the direct variation equation y = – 2 x. Its graph is shown.

GUIDED PRACTICE for Example 1 Write and graph a direct variation equation that has

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 =

GUIDED PRACTICE for Example 1 ANSWER Substituting – 3 for a in y = ax gives the direct variation equation y = – 3 x. Its graph is shown.

GUIDED PRACTICE for Example 1 Write and graph a direct variation equation that has

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 Write direct variation equation. 4 = a(– 7) Substitute 4 for y and – 7 for x. – 4 =a 7 Solve for a.

GUIDED PRACTICE for Example 1 ANSWER – 4 Substituting 7 for a in y

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

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) Substitute 3 for y and 5 for x. 3 =a 5 Solve for a.

GUIDED PRACTICE for Example 1 ANSWER Substituting 3 for a in y = ax

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

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) Substitute – 2 for y and 6 for x. – 1 =a 3 Solve for a.

GUIDED PRACTICE for Example 1 ANSWER Substituting– 1 for a in y = ax

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

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