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Alg1 Notes 8.6.notebook April 09, 2013
86 Solving Quadratic Equations by Factoring
Warmup WorksheetDo without talking for 15 minutes, then
compare answers EXCEPT for #9 12.
86 Solving Quadratic Equations by Factoring
1. Apply the zero product property to solve quadratic equations in factored form.2. Factor quadratic equations in order to solve.
In order to determine how manyseconds a diver will be in the air, they can use a quadratic equation.
Alg1 Notes 8.6.notebook April 09, 2013
I. The Zero Product Property
Let's play a game....
1. (x – 7)(x + 2) = 0x – 7 = 0 or x + 2 = 0 x = 7 or x = –2
The solutions are 7 and –2.
2. (x + 4)(x – 3) = 0
If a quadratic equation is written in standard form, ax2 + bx + c = 0,
then to solve the equation, you may need to factor before using the Zero Product Property.
Notice these quadratics were already in factored form.
II. Using Zero Product Property to Solve
Alg1 Notes 8.6.notebook April 09, 2013
3. x2 – 6x + 8 = 0 4. x2 + 4x = 21
Check Graph the related quadratic function. The zeros of the related function should be the same as the solutions from factoring.
III. Solve by Factoring
Pause for Your Graphing Calculator
x2 – 6x + 8 = 0Let's say we want to quickly check the answer to number 3:
1. Turn calculator ON2. Press Y= button3. Type in equation4. Press the GRAPH button5. Find the zeros by...
a. TABLE (above the GRAPH button)look for a zero in the Y1 column
b. CALC (above the TRACE button)arrow down to #2: zeroselect Left Bound by moving blinky left of the zeroselect Right Bound by moving blinky right of the zero Guess? Push Enter
Write these steps down...
Alg1 Notes 8.6.notebook April 09, 2013
To Solve x2 – 6x + 8 = 0 using your Graphing Calculator:
1. Turn calculator ON2. Press Y= button3. Type in equation4. Press the GRAPH button
*you may need to adjust the window. A shortcut is ZOOM button option 6. Otherwise, set the window manually using WINDOW button.
First Graph the corresponding function
To find the zeros, you can use TABLE or CALC
Find the zeros by...a. TABLE (above the GRAPH button)
look for a zero in the Y1 columnb. CALC (above the TRACE button)
arrow down to #2: zeroselect Left Bound by moving blinky left of the zeroselect Right Bound by moving blinky right of the zero Guess? Push Enter
Alg1 Notes 8.6.notebook April 09, 2013
6. –2x2 = 20x + 505. x2 – 12x + 36 = 0
IV. Solve With Your Calculator, Check
7. x2 – 6x + 9 = 0 8. x2 + 4x = 5
Solve by factoring algebraically, check graphically:
Alg1 Notes 8.6.notebook April 09, 2013
9. x2 + 4x = 5 10. 30x = –9x2 – 25
11. 30x = –9x2 – 25 12. 3x2 – 4x + 1 = 0
Solve by factoring algebraically, check graphically:
V. Application
The height in feet of a diver above the water can be modeled by h(t) = –16t2 + 8t + 8, where t is time in seconds after the diver jumps off a platform. Find the time it takes for the diver to reach the water.
Factor and solve...0 = –16t2 + 8t + 8
0 = –8(2t2 – t – 1)
0 = –8(2t + 1)(t – 1)
–8 ≠ 0, 2t + 1 = 0 or t – 1= 0
2t = –1 or t = 1t = –1/2 or t = 1
It takes the diver 1 second to reach the water.
Alg1 Notes 8.6.notebook April 09, 2013
The equation for the height above the water for another diver can be modeled by h = –16t2 + 8t + 24. Find the time it takes this diver to reach the water.
Factor and solve...
You Try!
It takes the diver 1.5 seconds to reach the water.
8.6 Page 565 #119 odd, 2337 odd,
41, 43, 45, 48, 49