EXAMPLE 5 Solve quadratic equations Solve a 3

EXAMPLE 5 Solve quadratic equations Solve (a) 3 x 2 + 10 x – 8 = 0 and (b) 5 p 2 – 16 p + 15 = 4 p – 5. a. 3 x 2 + 10 x – 8 = 0 (3 x – 2)(x + 4) = 0 3 x – 2 = 0 x= 2 3 Write original equation. Factor. or x + 4 = 0 or x = – 4 Zero product property Solve for x.

EXAMPLE 5 b. Solve quadratic equations 5 p 2 – 16 p + 15 = 4 p – 5. 5 p 2 – 20 p + 20 = 0 p 2 – 4 p + 4 = 0 (p – 2)2 = 0 p– 2=0 p=2 Write original equation. Write in standard form. Divide each side by 5. Factor. Zero product property Solve for p.

EXAMPLE 6 Use a quadratic equation as a model Quilts You have made a rectangular quilt that is 5 feet by 4 feet. You want to use the remaining 10 square feet of fabric to add a decorative border of uniform width to the quilt. What should the width of the quilt’s border be?

EXAMPLE 6 Use a quadratic equation as a model SOLUTION Write a verbal model. Then write an equation. 10 = 20 + 18 x + 4 x 2 – 20 0 = 4 x 2 + 18 x – 10 0 = 2 x 2 + 9 x – 5 0 = (2 x – 1)(x + 5) 2 x – 1 = 0 or x + 5 = 0 x = 1 or x = – 5 2 Multiply using FOIL. Write in standard form Divide each side by 2. Factor. Zero product property Solve for x.

EXAMPLE 6 Use a quadratic equation as a model ANSWER Reject the negative value, – 5. The border’s width should be 1 ft, or 6 in. 2

EXAMPLE 7 Solve a multi-step problem Magazines A monthly teen magazine has 28, 000 subscribers when it charges $10 per annual subscription. For each $1 increase in price, the magazine loses about 2000 subscribers. How much should the magazine charge to maximize annual revenue ? What is the maximum annual revenue ?

EXAMPLE 7 Solve a multi-step problem SOLUTION STEP 1 Define the variables. Let x represent the price increase and R(x) represent the annual revenue. STEP 2 Write a verbal model. Then write and simplify a quadratic function.

EXAMPLE 7 R(x) Solve a multi-step problem = = (– 2000 x + 28, 000)(x + 10) – 2000(x – 14)(x + 10)

EXAMPLE 7 Solve a multi-step problem STEP 3 Identify the zeros and find their average. Find how much each subscription should cost to maximize annual revenue. The zeros of the revenue function are 14 and – 10. The average of the zeroes is 14 + (– 10) = 2. 2 To maximize revenue, each subscription should cost $10 + $2 = $12. STEP 4 Find the maximum annual revenue. R(2) = – 2000(2 – 14) (2 + 10) = $288, 000

EXAMPLE 7 Solve a multi-step problem ANSWER The magazine should charge $12 per subscription to maximize annual revenue. The maximum annual revenue is $288, 000.

GUIDED PRACTICE for Examples 5, 6 and 7 Solve the equation. 19. 6 x 2 – 3 x – 63 = 0 ANSWER 3 1 or – 3 2 20. 12 x 2 + 7 x + 2 = x +8 ANSWER no solution 21. 7 x 2 + 70 x + 175 = 0 ANSWER – 5

GUIDED PRACTICE 22. for Examples 5, 6 and 7 What If ? In Example 7, suppose the magazine initially charges $11 per annual subscription. How much should the magazine charge to maximize annual revenue ? What is the maximum annual revenue ? ANSWER The magazine should charge $12. 50 per subscription to maximize annual revenue. The maximum annual revenue is $312, 500.