Find the area of a triangle two sides of which are 18 cm and 10 cm and the perimeter is 42 cm.

Two sides length are given, we need to figure out the length of this side.⇒Let x be length of third side⇒Perimeter=42 cm⇒18+10+x=42⇒x=42-28=14 cm⇒2s=42⇒s=21 cm⇒a=18,b=10,c=14⇒A=√s(s−a)(s−b)(s−c)⇒√21(21-18)(21-10)(21-14)=√21×3×11×7⇒A=21√11cm2