Sunday, March 6, 2011
Saturday, February 5, 2011
Form 2 - Directed Numbers
Directed Numbers
Numbers can either be positive or negative. Often brackets are put around negative numbers to make them easier to read, e.g. (-2). If a number is positive, the + is usually missed out before the number. So 3 is really (+3). Adding and multiplying combinations of positive and negative numbers can cause confusion and so care must be taken.
Addition and Subtraction
Two 'pluses' make a plus, two 'minuses' make a plus. A plus and a minus make a minus.Example
3 + (-2)A plus and a minus make a minus, so this is the same as 3 - 2 = 1
Example
(-2) + (-5) = -7This is the same as (-2) - 5 = -7
Multiplication and Division
If two positive numbers are multiplied together or divided, the answer is positive.If two negative numbers are multiplied together or divided, the answer is positive.
If a positive and a negative number are multiplied or divided, the answer is negative.
Examples
(-2) ÷ (-4) = ½(8) ÷ (-2) = (-4)
2 × (-3) = (-6)
(-2) × (-2) = 4
