Math Is Fun Forum

Peaches47

Member

Registered: 2008-02-17

Posts: 13

Heron's formula

Ok this one is use Heron's formula to find the area of the triangle.  It sounded like it was going to be complicated by the name but when I looked at how to work it out it seemed easy. 

here is the problem:  a=13 meters, b=19 meters, c = 10 meters So.......

to begin the Heron's formula I did this

s=1/2(a+b+c) = 1/2(13+19+10)=42 then

AREA= sqrt 42(42-13)(42-19)(42-10)
        = sqrt 896448

I think but, this is where I get lost.

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Struggling Middle Aged Math Student

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Heron's formula

You forgot to half the sides after adding them up.
If it helps you remember, think of the 's' as standing for 'semiperimeter'.

Using s=21 with the area formula gives that A = √(21x(21-10)x(21-13)x(21-19))
= √(21x11x8x2) = 4√(231) ≈ 61m².

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Why did the vector cross the road?
It wanted to be normal.

erwr

Guest

Re: Heron's formula

AREA= sqrt 42(42-13)(42-19)(42-10)
        = sqrt 896448

I think but, this is where I get lost.

Identity

Member

Registered: 2007-04-18

Posts: 934

Re: Heron's formula

I think there are a few more 'words' we ought to add to the censor.

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: Heron's formula

Th3r3 VV1ll allways bee differant wayz too spel b4d wurds 2 g3t ar0und chekers.  The point of the checker is to make sure people don't use one carelessly.

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

Peaches47

Member

Registered: 2008-02-17

Posts: 13

Re: Heron's formula

When reworking this problem correctly I get the same answe as you did Mathsyperson, however the mulitple choice answers dont reflect  61 meters.  they are  29, 116, 118 and 58 sq meters.

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Struggling Middle Aged Math Student

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Heron's formula

Hmm. I double-checked my answer and I got the same thing, so I think you're probably just meant to go for 58m.

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Why did the vector cross the road?
It wanted to be normal.

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Heron's formula

Maybe the orginal problem was a typo.
Maybe it said a=13, b = 16, and c = 9. 
That comes out to 58.4 something.

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igloo myrtilles fourmis