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March 24th, 2009, 06:15 AM
| | Super Member | | Join Date: May 2006 Location: Lexington, MA (USA)
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| |  Mathematical Side Show - 2
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March 25th, 2009, 11:22 AM
|  | He's dead, Jim | | Join Date: Jan 2008 Location: Big Stone Gap, Virginia
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1 x 8 + 1 = 9
12 x 8 + 2 = 98
123 x 8 + 3 = 987
1234 x 8 + 4 = 9876
12345 x 8 + 5 = 98765
123456 x 8 + 6 = 987654
1234567 x 8 + 7 = 9876543
12345678 x 8 + 8 = 98765432
123456789 x 8 + 9 = 987654321
1 x 9 + 2 = 11
12 x 9 + 3 = 111
123 x 9 + 4 = 1111
1234 x 9 + 5 = 11111
12345 x 9 + 6 = 111111
123456 x 9 + 7 = 1111111
1234567 x 9 + 8 = 11111111
12345678 x 9 + 9 = 111111111
123456789 x 9 +10= 1111111111
9 x 9 + 7 = 88
98 x 9 + 6 = 888
987 x 9 + 5 = 8888
9876 x 9 + 4 = 88888
98765 x 9 + 3 = 888888
987654 x 9 + 2 = 8888888
9876543 x 9 + 1 = 88888888
98765432 x 9 + 0 = 888888888
1 x 1 = 1
11 x 11 = 121
111 x 111 = 12321
1111 x 1111 = 1234321
11111 x 11111 = 123454321
111111 x 111111 = 12345654321
1111111 x 1111111 = 1234567654321
11111111 x 11111111 = 123456787654321
111111111 x 111111111=123456789 87654321
__________________ He who knows not and knows not that he knows not is a fool, shun him. He who knows not and knows that he knows not is a child, teach him. He who knows and knows not that he knows is asleep, wake him. And he who knows and knows that he knows is wise, follow him.
-- Persian Proverb
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March 25th, 2009, 11:32 AM
| | He's dead, Jim | | Join Date: Jan 2008 Location: Big Stone Gap, Virginia
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The 7 - 11 - 13 trick.
Pick any 3 digit number. (ex. 123)
Multiply by 7
Then, multiply that answer by 11
Then multiply that answer by 13
Result: 123123
__________________ He who knows not and knows not that he knows not is a fool, shun him. He who knows not and knows that he knows not is a child, teach him. He who knows and knows not that he knows is asleep, wake him. And he who knows and knows that he knows is wise, follow him.
-- Persian Proverb
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![(a^2+b^2)(c^2+d^2) \;=\;\begin{array}{c}(ac+bd)^2 + (ad-bc)^2 \\ \\[-4mm] (ad+bc)^2 + (ac-bd)^2 \end{array}](http://www.mathhelpforum.com/math-help/latex2/img/4a7ddcf3ca299b4d38f69e1929b07516-1.gif "(a^2+b^2)(c^2+d^2) \;=\;\begin{array}{c}(ac+bd)^2 + (ad-bc)^2 \\ \\[-4mm] (ad+bc)^2 + (ac-bd)^2 \end{array}")
