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Quit

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Divisors Friendly Numbers Sociable Numbers Quadratic Formula

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Quit Divisors are all the numbers which divide evenly into a number including the number 1, but not including the number itself in the case of friendly and sociable numbers Therefore the divisors of 24 are 1, 2, 3, 4, 6, 8 and 12 They sum to 36 Divisors

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These are pairs of numbers such that each number is the sum of the divisors of the other number. Talismen sold in the middle ages would be inscribed with these numbers, on the grounds that they would promote love. An Arab mathematician claims that people would write one of the pair of numbers on one fruit and eat it, writing the second number on another fruit and give it to a lover as a mathematical aphrodisiac! Friendly Numbers

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Quit Friendly Numbers There was only one pair discovered until Fermat discovered the pair 17,296 and 18,416 in 1636 Descartes discovered the pair 9,363,584 and 9,437,056 in 1638 In 1866 a sixteen year old Italian found the pair 1184 and 1210 Computers can be programmed to find larger ones now!

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QuitProject The divisors of 1184 are 1, 2, 4, 8, 16, 32, 37, 74, 148, 296, 592 Sum = 1210 The divisors of 1210 are 1, 2, 5, 10, 11, 22, 55, 110, 121, 242, 605 Sum = 1184

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Quit Sociable Numbers These are groups of three or more numbers which form closed loops The sum of the divisors of the first give the second The sum of the divisors of the second give the third and so on until the divisors of the last give the first number

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Quit Quadratic formula The Quadratic formula works to factorise all equations of the form ax 2 + bx + c = 0 The roots are: ––––––––––––– – b b – 4ac 2a2a x = ––––––

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Quit a = 1 b = 9 c = 20 (9) 2 4(1)(20) 2(1) x = (9) x 2 + 9x + 20 = 0 b 4ac 2 2a2a x = b b 81 – 80 2 = 9 1 2 = 2 = 9 1 8 2 = x = 4 or – 5 or 10 2

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Quit The area of a rectangle is 77 cm 2. One side is 4 cm longer than the other. Find the length and breadth of the rectangle. Area = 77 cm 2 x + 4x + 4 x x 2 + 4x – 77 = 0 x(x + 4x) = 77

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Quit a = 1 b = 4 c = – 77 (4) 2 4(1)(–77) 2(1) x = (4) x 2 + 4x – 77 = 0 b 4ac 2 2a2a x = b b x = or – 11 or = 4 = 4 2 = 4 18 = 14 2

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