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# 5-4 Notes: Writing a Function Rule

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## Presentation on theme: “5-4 Notes: Writing a Function Rule”— Presentation transcript:

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5-4 Notes: Writing a Function Rule

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Example 1: Writing a Function Rule from a Table
What do you do to x to get f(x)? X f(X) 1 5 2 6 3 7 4 8 Relate: f(x) equals x plus 4 f(x)= x + 4

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2. x y 1 3 9 6 36 81 Relate: y equals x times itself y = x2

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3. x f(x) 1 -1 2 3 4 Relate: f(x) equals x minus 2 f(x)= x-2

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4. x y 1 2 4 3 6 8 Relate: y equals x times 2 y = 2x

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5. x y 1 3 2 4 5 6 Relate: y equals x plus 2 y = x + 2

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Example 2: Real World Problem Solving
A carpenter buys finishing nails by the pound. Each pound of nails costs \$1.19. Write a function rule to describe this relationship. Relate: cost equals 1.19 times nails (x) C(x) = 1.19x

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C(12)=1.19 (12) \$14.28 How much do 12lb of finishing nails cost?
2. From problem 1. c(x)= 1.19x: How much do 12lb of finishing nails cost? C(12)=1.19 (12) \$14.28

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Relate: profit is \$18 times lawns mowed minus cost of mower.
3. Suppose you borrow money from a relative to buy a lawn mower that costs \$245. You charge \$18 to mow a lawn. Write a rule to describe your profit as a function of the number of lawns mowed. Relate: profit is \$18 times lawns mowed minus cost of mower. Define: let n=number of lawns mowed & p=profit p(n)=18n-245

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Define: let h=number of hours & p=total profit p(h)=15h-199
4. Suppose you buy a word-processing software package that costs \$199. You charge \$15 per hour for word processing. Write a function rule to describe your profit as a function of the number of hours you work. Relate: total profit is \$15 times number of hour of word processing minus cost of word processor. Define: let h=number of hours & p=total profit p(h)=15h-199

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HW # 14 Page 256 (1-18)

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Definition of a Function A function is a set of ordered pairs in which no two ordered pairs of the form (x, y) have the same x-value with different y-values.

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