Question

two sides of triangles are 13 cm and 14cm and semi perimeter is 18 cm find third side of a triangle

Answer 1

(13+14+X)/2=18
X=9 on solving

Answer 2

Let the unknown  side be X

So (X + 13 + 14 )/2 = 18 as per the question

So we have X + 27 = 36

So X = 9 cm
Hence 9cm is third side.