Use Heron's formula, which takes the form of S=(a+b+c)/2
Heron’s Formula Example
For a triangle with sides a =4 b = 3, and c = 5:
s = (4+3+5)/2
s = (12)/2
s = 6
Area = sqr(s(s-a)(s-b)(s-c). Replace Area in the equation with its equivalent in the area formula: 1/2bh (or 1/2ah or 1/2ch).
Solve for h. For our example triangle this looks like:
1/2(3)h = sqr(6(6-4)(6-3)(6-5).
3/2h = sqr(6(2)(3)(1)
3/2h = sqr(36)
Use a calculator to calculate the square root, which in this case makes it 3/2h = 6.
Therefore, height is equal to 4, using side b as the base.
Now, substitute your values into the formula.
