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Just a tiny addition (Posted on 2014-11-18) Difficulty: 2 of 5
Wihout changing the order, add a single digit or a mathematical sign (but not both) to make true the expression below:

(71-1)*(71+1)=7

See The Solution Submitted by Ady TZIDON    
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Solution answer(s) Comment 5 of 5 |
(71-1)*(71+1) ≧ 7 : adding the 'greater than' sign makes the expression true. 
Note: (71-1)*(71+1) = 5040
5040 ≧ 7.

(71-1)*(71+1) ¬= 7 : the  ¬, !, and ~ can each be used for negation. The sign, or symbol, ¬ is noted to be the preferred choice.
5040 ¬= 7, (in ASCII notation, this is sometimes written as 5040 <> 7).

If permitted to change a symbol by adding a symbol used in mathematical notation, then there are two more solutions:

Adding a 'minus sign' over the 'equal sign' to make a 'congruence' symbol:
(71-1)*(71+1) ≡ 7  (mod 719) : the modulus notation may be omitted when the modulus m is understood in context with the use of congruence, thus this may be considered a valid option for a true expression, as well.

Overlaying the ASCII symbol for division, /, over the 'equal sign' to make a 'not equal' symbol.
(71-1)*(71+1) ≠ 7
(Other 'not equal' notations are already mentioned or demonstrated earlier.)

Edited on November 19, 2014, 7:27 am
  Posted by Dej Mar on 2014-11-19 07:15:04

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