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The A to Z’s of Math Activities N is for Negative Number Background A negative number is a number with a value less than zero. It is usually written with a minus sign (-) in front of it. Numbers greater than zero are positive numbers. They can be written with a plus sign (+). Any number that is not preceded by a sign is a positive number. In mathematical terms a minus sign (-) can also mean subtract; while a plus sign (+) can refer to addition. Historically, negative numbers were first written about during China’s Han Dynasty (202 BC to 220 AD). Materials Vocabulary Activity 1 Minus represented by – Circle Patterns can mean (1) negative number or (2) Red and green crayons take away, subtract Scissors Negative number a number less than Activity 3 zero Graph paper Plus represented by + Ruler Can mean (1) positive number or (2) keep, addition Positive number a number greater than zero Zero indicates no value Activity 1 SET UP circle pattern sheet, red and green crayons, scissors Color half of the circles red and half of the circle green, cut out the circles Circle Patterns OOOOOO OOOOOO The A to Z’s of Math Activities N is for Negative Number OOOOOO OOOOOO Activity 1 Combine Positive and Negative Numbers Write problem on the white board Example: -3 + (+2) STEP ONE Use circles to represent the numbers Red circles represent negative numbers Green circle represent positive numbers Set out 3 red and 3 green circles, next to each other Set out 2 red circles and 2 green circles, next to each other STEP TWO Begin with -3 Remove the 3 green/positive circles The A to Z’s of Math Activities N is for Negative Number STEP THREE What is the problem asking you to do? Answer: add or keep STEP FOUR Keep the +2 Remove the 2 red/negative circles STEP FIVE Partner up, remove pairs of one red and one green circle until only one color remains STEP SIX What is the answer? Answer: There is one red remaining so the answer is - 1 (If there were none left, the answer would be zero) The A to Z’s of Math Activities N is for Negative Number Try it again Write problem on the white board Example: -4 - (-1) STEP ONE Use circles to represent the numbers Red circles represent negative numbers Green circle represent positive numbers Set out 4 red and 4 green circles, next to each other Set out 1 red circle and 1 green circle, next to each other STEP TWO Begin with -4 Remove the 4 green/positive circles STEP THREE What is the problem asking you to do? Answer: subtract or take away The A to Z’s of Math Activities N is for Negative Number STEP FOUR Take away the -1 Remove the 1 red/negative circle STEP FIVE Partner up, remove pairs of one red and one green circle until only one color remains STEP SIX What is the answer? Answer: There are three red remaining so the answer is -3 Additional problems: +3 + (-2) = +1 -3 + (-2) = -5 +3 – (+2) = +1 +4 – (-1) = +5 +4 + (+1) = +5 -4 – (-1) = -3 +2 + (+2) = + 4 -2 + (+2) = 0 +2 – (-2) = +4 Activity 2 Think about it Have students work in small groups Review problems and answers on the white board Ask students what they observe The A to Z’s of Math Activities N is for Negative Number Possible answer: A negative negative equals a positive (Comparative to a double negative when you speak) A negative sign telling you what to do will change the sign of the next number Activity 3 Optical Illusion SET UP Graph paper, ruler, pencil, pen STEP ONE Use the ruler to draw two intersecting lines in pen Draw the lines in the middle of the graph paper STEP TWO Use a pencil; mark the space where the lines intersect 0 STEP THREE Use a pencil; begin at the 0 and move right, number each line +1to +11 These numbers represent values MORE than zero STEP FOUR Use a pencil; begin at the 0 and move left, number each line -1 to -11 These numbers represent values LESS than zero STEP FIVE Use a pencil; begin at the 0 and move up, number each line +1to +11 These numbers represent values MORE than zero STEP SIX Use a pencil; begin at the 0 and move down, number each line -1 to -11 These numbers represent values LESS than zero The A to Z’s of Math Activities N is for Negative Number STEP SEVEN Use the ruler and the pen to connect pairs of numbers: Note: the first number represents the numbers on the left to right line the second number represents the numbers on the up and down line (left to right line, up and down line) (+1, +11) (+2, +10) (+3, +9) (+4, +8) (+5, +7) (+6, +6) (+7, +5) (+8, +4) (+9, +3) (+10, +2) (+11, +1) (-1, +11) (-2, +10) (-3, +9) (-4, +8) (-5, +7) (-6, +6) (-7, +5) (-8, +4) (-9, +3) (-10, +2) (-11, +1) (+1, -11) (+2, -10) (+3, -9) (+4, -8) (+5, -7) (+6, -6) (+7, -5) (+8, -4) (+9, -3) (+10, -2) (+11, -1) (-1, -11) (-2, -10) (-3, -9) (-4, -8) (-5, -7) (-6, -6) (-7, -5) (-8, -4) (-9, -3) (-10, -2) (-11, -1) STEP EIGHT Erase the pencil marks The A to Z’s of Math Activities N is for Negative Number Why do the lines appear curved? Answer: It’s an optical illusion Extension Find out what other discoveries were made by ancient China. Use Activity 3 as an introduction to Cartesian plane and coordinate points. What is an optical illusion? Find one to share with the class.

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