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Exercise Solve. 5 = 3x x = 5 3
Exercise Solve. 4 = k 1 3 k = 12
Exercise Solve. y 25 3 5 = y = 15
Exercise Solve. 3 5 25 x = x = 41 2 3
Exercise If 4 = 6k, what is the value of 3k? 2
Direct Variation A direct variation is formed by the variables x and y if the ratio y : x always equals a constant k, where k is a positive number.
Directly ProportionalVariables are directly proportional when y is said to vary directly with x.
Constant of ProportionalityThe constant k is the constant of variation, or the constant of proportionality.
x hours y miles y x 1 30 2 60 3 90 4 120
Example 1 Does y vary directly with x in the following table? If so, find the constant of variation and write an equation for the direct variation. x y 1 3 3 9 5 15 7 21
x y 1 3 3 9 5 15 7 21 = 3 1 y x 3 = 21 7 y x 3 = 9 3 y x 3 = y x 3 k y = kx = 15 5 y x 3 y = 3x
Constant of Variation The constant of variation is the steady rate of change. The constant k is the constant of variation, or the constant of proportionality.
Example 2 Indicate which equations represent a direct variation. If an equation describes a direct variation, give the constant of variation. f(x) = 2.2x direct variation; k = 2.2
y = 4x − 1 This is not a direct variation; the variable must be a multiple of x. d = 45t This is a direct variation; k = 45. y = −2x This is not a direct variation; the coefficient of x must be positive.
y = mx + b y = kx
Example 3 Graph the direct variation y = 4x. x −1 1 y −4 4
Example 4 Find k if y varies directly with x and y = 12 when x = . Write an equation for the direct variation. 1 2 y = kx k = 24 12 = k( ) 1 2 y = 24x 2(12) = k( )(2) 1 2
Example 5 If y varies directly with x and y = 6 when x = 2, find y when x = . 2 3 y = kx y = 3x y = 3( ) 2 3 6 = k(2) 3 = k y = 2
Example Find k if y varies directly with x and y = 14 when x = 4.
Example Find k if y varies directly with x and y = 15 when x = 2.
Example If y varies directly with x and y = 7 when x = 1, find y when x = 6. y = 42
Example If y varies directly with x and y = 27 when x = 15, find y when x = 6. 54 5 y =
Example Indicate which equations represent a direct variation. If an equation describes a direct variation, give the constant of variation. If not, explain.
y = 4x Yes. k = 4. y = 3x + 5 No. The y-intercept is not zero. y = −4x No. The slope is not positive.
2-3 Direct Variations.
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Direct Variation Objective: Students will be able to identify, write and graph direct variation equation.
Direct Variation. A direct variation is… A linear equation The y-intercept must be zero!!!! The graph of a direct variation will ALWAYS go through the.
1 Math Supplement The Proportionality A “is proportional to” B.
Language Goal Students will be able to verbally express direct variation. Math Goal Students will be able to identify, write, and graph direct variation.
5-2 Direct Variation A direct variation is a relationship that can be represented by a function in the form y = kx, where k ≠ 0. The constant of variation.
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Vocabulary direct variation inverse variation
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Direct Variation y = mx (no b) Lines that go through the origin Y intercept of zero Slope also called constant of variation (variation constant)
Review after Christmas!. Solve the below equations for the variable..5 (6x +8) = 16 1.
Equations of Lines Equations of Lines
I can write and graph an equation of a direct variation by identifying the constant of variation.
2.4 Writing Equations of Lines p. 91. Learning Target I can write equations of a line.
2.4 Writing Equations of Lines. We’ve learned to graph given an equation. Now we’ll learn to write the equation given the graph There are three ways.
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Slope and Direct Variation Lesson 5-2. ____________ ______________ is an equation in the form of ________, where k≠0. In the equation y = kx, ____ is.
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