Directed number
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Transcript of Directed number
A Directed Number…
• Is one which has a + or – sign attached
• To show its direction
+2-2
Positive & Negative numbers
NOT Plus & Minus numbers
Yes!
NO!
Try these
0 1 2 4 5 63-6 -5 -4 -3 -2 -1
a) +3 + -7b) +6 + -3c) -2 + -4d) -1 + +6
-4+3-6
+5
Think of 1st number as a starting point
Think of 2nd number as a move left or right
4 Volunteers with WHITEBOARDS
• How good a teacher am I?
• Give a mark between 1 and 10
• Hold up your boards – show class
SUBTRACT a NEGATIVE means ADD
Try these
0 1 2 4 5 63-6 -5 -4 -3 -2 -1
a) +3 - -2b) +1 - -3c) -2 - +4
+5+4-6
Think of 1st number as a starting point
Think of 2nd number as a move left or right
Think of SUBTRACT as a REVERSE of DIRECTION
Basic RulesADD a POSITIVE means ADD
ADD a NEGATIVE means SUBTRACT
SUBTRACT a POSITIVE means SUBTRACT
SUBTRACT a NEGATIVE means ADD
+ +3 = + 3
+ -3 = - 3
- +3 = - 3
- -3 = + 3
Sometimes Textbooks give a number in a bracket
5 - (+2) = 5 - +2
5 - (+2)
Sometimes Textbooks give the sign NOT raised
= 5 - (+2) = 5 - +2
Rule for MultiplicationPOSITIVE x POSITIVE = POSITIVE +2 x +3 = +6
+2 x -3 = -6POSITIVE x NEGATIVE = NEGATIVE
-2 x -3 = +6NEGATIVE x NEGATIVE = POSITIVE
NEGATIVE x POSITIVE = NEGATIVE -2 x +3 = -6
If SAME SIGN, answer is POSITIVE
Rule for DivisionPOSITIVE ÷ POSITIVE = POSITIVE +18 ÷ +3 = +6
+18 ÷ -3 = -6POSITIVE ÷ NEGATIVE = NEGATIVE
-18 ÷ -3 = +6NEGATIVE ÷ NEGATIVE = POSITIVE
NEGATIVE ÷ POSITIVE = NEGATIVE -18 ÷ +3 = -6
If SAME SIGN, answer is POSITIVE
Inverse of Multiplication
Puzzle
• Can you complete this puzzle?
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Examples
If t = 3q + 4
If q = 5
If q = -5
t = 3x5 + 4
t = 3q + 4
3q = 3 x q
t = 15 + 4 t = 19
t = 3x-5 + 4 t = -15 + 4 t = -11
NOT t = 35 + 4 = 39