Page 128 - Math Course 3 (Book 1)

Direct Variation Equation

Graph a Direct Variation
2
Graph y = 2x. Graph y = – x.
3

A. B. A. B.
2
y = – x
3
2
y = 2x y = – x
3

y = 2x

C. D. C. D.

2
y = 2x y = – x
3

2
y = 2x y = – x
3

Answer Answer

MO. 4 - L2b

Solving Direct Variation

Equation

Let’s Begin –3 = k Simplify.

Therefore, the direct variation
Answer
Write and Solve a Direct Variation Equation equation is y = –3x.

Example Use the direct variation equation to find x when
y = 15.

y = kx Direct variation equation
Suppose y varies directly as x, and y = 9 when
x = –3. Write a direct variation equation that 15 = k(–3) Replace y with 15.
relates x and y.
15 = k(–3) Divide each side by –3.

Find the value of k. 3 3
–5 = x Simplify.
y = kx Direct variation formula

9 = k(–3) Replace y with 9 and x with –3. Answer Therefore, x = –5 when y = 15
9 k(–3)
3 = 3 Divide each side by –3.

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