The two equal sides of an isosceles triangle is 20 cm each and the third sides is 30 cm. What is the area (in \(cm^{2}\)) of the triangle?

75\(\sqrt{7}\)

Area =  \(\frac{b}{2}\sqrt{4a^{2}-b^{2}}\)

A = \(\frac{30}{4}\sqrt{4(20)^{2} - (30)^{2}}\) 

A = \(\frac{30}{4}\sqrt{1600 - 900}\)  

A = \(\frac{30}{4}\sqrt{700}\) = \(\frac{300}{4}\sqrt{7}\) = 75\(\sqrt{7}\) cm