Question

find the area of triangle two sides of which are 8 cm and 10cm and perimeter is 42 CM

Answer 1

area of triangle = root s(s-a)(s-b)(s-c)
here s is semi perimeter and a,b,c are the sides of triangle
given a=8cm,b=10cm and perimeter=42cm
semi perimeter=42/2=21cm
s=21cm
now perimeter=42cm
a+b+c=42cm
8cm+10cm+c=42cm
18cm+c=42cm
c=42-18=24cm
area of triangle=root s(s-a)(s-b)(s-c)
      root 21(21-8)(21-10)(21-24)
       root 21*13*11*-3

Answer 2

perimeter = 42cm

a+b+c = 42cm

18+10+c = 42cm

28+c = 42cm

c = (42-28)cm

c = 14cm

semi-perimeter = 42/2cm

= 21cm

area = s(s-a)(s-b)(s-c)

= 21/11cm2

(by heron formula)