Question

find the area of an isosceles triangle whose equal sides are 12 cm each and the perimeter is 30 cm

Answer 1

area of issoceles traingle is = 1/2 ×base× height.
parimeter of issoceles traingle = l×b=30
so , l=30/b=30/12 = 5/2= 2.5 cm
so area =1/2×2.5×12= 15 cm.

Answer 2

if the equal sides are 12 cm each, then

perimeter = sum of all sides

here, 30= 12+12+(non-parallel side)

30-24= non-parallel side 

6=  non- parallel side 

then 

semi perimeter = 30/2 = 15

then, area by heron's formula,

area = root [15*(15-12)(15-12)(15-6)

area = root [15*3*3*9]

area = 3*3*root(15)

area= 9root 15

area = 34.85..

i hope this will help