The sides of a triangle measure $15 \text{ cm}$,$17 \text{ cm}$,and $20 \text{ cm}$. Then,the semi-perimeter of the triangle is ......... $\text{cm}$.

According to Heron's formula,the area of a triangle $=$ ...........

In a right-angled triangle,the length of the hypotenuse is $29\,cm$ and one of the sides forming the right angle is $21\,cm$. Then,the semi-perimeter of the triangle is ............ $cm$.

Find the area of a triangle whose sides are $13\, cm$,$14\, cm$,and $15\, cm$. (in $, cm^2$)

The perimeter of an equilateral triangle is $60 \, m$. The area is

Write True or False and justify your answer.
If $a, b, c$ are the lengths of three sides of a triangle, then area of a triangle $= \sqrt{s(s-a)(s-b)(s-c)}$, where $s = \text{perimeter of triangle}$.