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Triangles with no area (Posted on 2009-12-30) Difficulty: 1 of 5
A little disconcertingly I generated the data of a triangle with integral sides in a spreadsheet. The area calculation suggested that it had zero area.

Knowing there was an obvious contradiction I wrote a computer listing to see if there were others which fitted this situation, and yes, there was an infinite number.

Clearly I am doing something wrong, explain.

  Submitted by brianjn    
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Solution: (Hide)
Given values a, b and c as sides of a triangle none of those values may equal half of their sum.

In Heron's formula for calculation of area that condition would produce a multiplier which is zero!

My original spreadsheet read something like:
a  b  c  s     A
1  2  3  3     0    Note this one
2  3  4  4.5   2.90473751
3  4  5  6     6
4  5  6  7.5   9.921567416
5  6  7  9    14.69693846
6  7  8 10.5  20.33316257
7  8  9 12    26.83281573
where in Heron's formula for triangular area we have:
A= √s(s-a)(s-b)(s-c)

The following listing generates data for all "triangles" having "zero" area with a maximum side of 50 units.
CLS
OPEN "notri.txt" FOR OUTPUT AS #1

 FOR a = 1 TO 50
  FOR b = 1 TO 50
    FOR c = 1 TO 50

    s = (a + b + c) / 2
    m = (s * (s - a) * (s - b) * (s - c))
  
    IF m = 0 THEN
    PRINT a; b; c; s; m
    PRINT #1, a; b; c; s; m
    END IF
 
    NEXT: NEXT: NEXT

CLOSE 1

Comments: ( You must be logged in to post comments.)
  Subject Author Date
re(2): Removal?brianjn2010-01-01 20:04:08
re: Removal?Jer2010-01-01 14:15:17
Removal?brianjn2009-12-31 20:15:46
re(3): most likely way - and apologyCharlie2009-12-31 13:23:39
re(2): most likely way - and apologybrianjn2009-12-30 23:52:06
re(3): most likely waybrianjn2009-12-30 20:10:03
re(2): most likely wayCharlie2009-12-30 19:18:44
re: most likely waybrianjn2009-12-30 19:04:37
Some Thoughtsmost likely wayCharlie2009-12-30 13:44:29
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