Question

what is the formula used to get the area of a triangle knowing the measure of its sides a, b, c?

Answer 1

you can use "heron's formula"

Answer 2

area = sqrt(s(s-a)(s-b)(s-c)
if my memory serves me right

Answer 3

http://en.wikipedia.org/wiki/Heron%27s_formula

Answer 4

jimmyrep has it. of course you need to know what "s" is

Answer 5

where s = sum of the 3 sides / 2

Answer 6

First find p, the perimeter of the triangle by adding all three sides. Then use sqrt(p(p-a)(p-b)(p-c)) where a, b, and c are sidelengths.

Answer 7

"semiperimeter" good word that, even if spell check doesn't like it

Answer 8

@smoothmath it is not p, it is what jimmyrep said

Answer 9

ok ok then a complete equation would be?

Answer 10

jimmyrep has it or look at the wiki entry. it has it all written out

Answer 11

\[A = \sqrt{s(s - a)(s - b)(s - c)},\]where s = (a + b + c)/2 [Heron's formula]

Answer 12

area = sqrt[(s(s-a)(s-b)(s-c)]

Answer 13

yep abtrehearn has it too

Answer 14

you can also find one of the angles using the law of cosine and then use
\[Area=\frac{1}{2}ab\sin(C)\]

Answer 15

thank you all, now I would like to know how would it look like in 3 dimensions adding z to the formula, that is volume. Then how can I calculate the weight of that 3d object by knowing the average density of it?

Answer 16

If you rewrite the formula without the s and express only in terms of a, b, and c, then
\[A = (1/4)\sqrt{(a + b + c)(-a + b + c)(a - b + c)(a + b + c)}.\]

Answer 17

\[(1/4)\sqrt{(a + b + c)(-a + b + c)(a - b + c)(a - b - c)}.\]

Answer 18

but now I have a,b,c,d,e,f, its a pyramid

Answer 19

ooh I found it, in wikipedia 5.1 Heron-looking formula for tetrahedra