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# 2 4mult Pos By Neg

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### 2 4mult Pos By Neg

1. 1. Multiplication of Integers Chapter 2.4 Algebra I Pg 73-77
2. 2. Warm-Up
4. 4. What’s the Deal? <ul><li>In today’s lesson we will review multiplication and division of signed numbers. </li></ul>
5. 5. What and why? <ul><li>7 x -5 = - 35 </li></ul><ul><li>+7 x +5 = +35 </li></ul><ul><li>-7 x 5 = - 35 </li></ul><ul><li>-7 x -5 = + 35 </li></ul><ul><li>Multiplication is fast adding. </li></ul><ul><li>-5 + -5 + -5 + -5 + -5 + -5 + -5 = -35 </li></ul><ul><li>5 + 5 + 5 + 5 + 5 + 5 + 5 = 35 </li></ul><ul><li>-7 + -7 + -7 + -7 + -7 = - 35 </li></ul><ul><li>- (-7 + -7 + -7 + -7 + -7) = - (-35) </li></ul>
6. 6. Count the Negatives <ul><li>7 x -5 = - 35 </li></ul><ul><li>+7 x +5 = +35 </li></ul><ul><li>-7 x 5 = - 35 </li></ul><ul><li>-7 x -5 = + 35 </li></ul><ul><li>Count the negative signs.. </li></ul><ul><li>Ask Odd or Even ? </li></ul><ul><li>Odd? </li></ul><ul><ul><li>Negative Answer </li></ul></ul><ul><li>Even? </li></ul><ul><ul><li>Positive Answer </li></ul></ul><ul><li>This works the same for division. </li></ul>
7. 7. Number Families <ul><li>Factor x Factor = Product </li></ul><ul><li>F x F = P </li></ul><ul><li>Product / Factor = Factor </li></ul><ul><li>P / F = F </li></ul>
8. 8. Number Families <ul><li>-8 * 5 = -40 </li></ul><ul><li>-5 * 8 = -40 </li></ul><ul><li>-40 / 5 = -8 </li></ul><ul><li>-40 / 8 = -5 </li></ul><ul><li>-8 * -5 = 40 </li></ul><ul><li>-5 * -8 = 40 </li></ul><ul><li>40 / -5 = -8 </li></ul><ul><li>40 / -8 = -5 </li></ul>negative / positive = negative positive / negative = negative
9. 9. Try Some <ul><li>-11 * + 5 = </li></ul><ul><li>-7 * - 10 = </li></ul><ul><li>+6 * - 5 = </li></ul><ul><li>-7 * + 8 = </li></ul><ul><li>- 35 / - 5 = </li></ul><ul><li>+ 63 / - 9 = </li></ul><ul><li>- 56 / - 7 = </li></ul><ul><li>+ 32 / - 8 = </li></ul>
10. 10. Try Some - answers <ul><li>-11 * + 5 = - 55 </li></ul><ul><li>-7 * - 10 = + 70 </li></ul><ul><li>+6 * - 5 = - 30 </li></ul><ul><li>- 7 * + 8 = - 56 </li></ul><ul><li>- 35 / - 5 = +7 </li></ul><ul><li>+ 63 / - 9 = -7 </li></ul><ul><li>- 56 / - 7 = +8 </li></ul><ul><li>+ 32 / - 8 = -4 </li></ul>
11. 12. Part Two Fractions and Reciprocals
12. 13. Multiply fractions 1 2 3 2
13. 14. Reciprocals are used for dividing fractions. What’s a reciprocal?
14. 15. Multiply a number by its reciprocal to get an answer of +1 What’s the reciprocal of 7 / 8 ? 8 / 7
15. 16. Using Reciprocals <ul><li>Reciprocals are useful for dividing fractions. </li></ul><ul><li>Rewrite the division of a fraction using multiplication by the reciprocal of the 2 nd number. </li></ul>
16. 17. Rewrite these number sentences.
17. 18. Rewritten number sentences One is your friend. Use 1 to make whole numbers into fractions.
18. 19. Keep fighting, Go Tigers