A piece of art is in the shape of an equilateral triangle with sides of 21 in. What is the area of the piece of art to the nearest tenth?

311.8 in.^2
381.9 in.^2
155.9 in.^2
191.0 in.^2

Please help?

4 answers

let s be half the perimeter, or 63/2

area=sqrt[s*(s-21)(s-21)(s-21)l
area= sqrt(63/2*(21/2)^3)
= sqrt(21*3/2 ( 21/2)^3
= 21*21/2 sqrt3=190.958602
= 191.0 to the nearest tenth.

Thank you, bob!!!:)

wot does s stand for

191.0