Question

in ∆ABC,D,E and F are the midpoint of Ab ,bc and ca respectively. if ab=6cm,bc=7.2cm and ca=7.8cm,find the perimeter of ∆DEF

Answer 1

Given that D E F are midpoints of TriangleABC
Then,
the perimeter of triangleDEF would be half the perimeter of Triangle ABC
perimeter of triangle ABC =6+7.2+7.8=21cm
perimeter of triangle DEF= 21/2=10.5cm

Answer 2

Given:triangle ABC, D, E and F are the midpoints of sides AB, BC, CA. 
If AB = 6 cm, BC = 7.2 cm and AC = 7.8 cm
to find the perimeter of triangle DEF. 

soln: AB = 6 implies AD = 3 
AC = 7.8 implies CF = 3.9 

AB + AC + BC = P 
6 + 7.8 + BC = 21 
BC = 21 - 6 - 7.8 
BC = 7.2 
BE = BC / 2 
BE = 7.2 / 2 
BE = 3.6

perimeter = (6+7.2+7.8)/2
= 21/2
=10.5 cm