For sine formula , you need to remember "the lengths of the sides of an arbitrary triangle to the sines of its angles"
a/ sin A = b/ sin B = c/ sin C
where a, b, and c are the lengths of the sides of a triangle, and A, B, and C are the opposite angles.
the cosine law relates the lengths of the sides of a triangle to the cosine of one of its angles.
c^2 = a^2+b^2-2ab cos C
where C denotes the angle contained between sides of lengths a and b and opposite the side of length c.
Heron's formula :
sqrt (s(s-a)(s-b)(s-c))
when s= 0.5(a+b+c)
REF:
http://mathworld.wolfram.com/HeronsFormula.html
http://www.mathsisfun.com/geometry/herons-formula.html
en.wikipedia.org