Let a, b and c are the sides of triangle and s is
the semi-perimeter, then its area is given by:
A = \(\sqrt{s(s-a)(s-b)(s-c)}\)where s = \(\frac{a+b+c}2\)[Heron’s Formula]
s = \(\frac{a+b+c}2\) = \(\frac{3+4+5}2\) = 6
A = \(\sqrt{6(6-3)(6-4)(6-5)}\)
A = \(\sqrt{6\times3\times2\times1}\) = 6 cm2