Find the area of a triangle whose side lengths are 35 cm, 28 cm and 21 cm.

You can act using Heron’s formula.
It is written using the radical on the right side, but since I don’t know how best to show this, I’ll write it down better without the root sign, but at the same time it is necessary to raise the Area to the second power.
S ^ 2 = p * (p-a) * (p-b) * (p-c), where
S is the area of the triangle,
a, b, c- sides of a triangle
p is a semi-perimeter, i.e. (a + b + c) / 2
We know all sides of the triangle 35.28.21 cm
Find a semi-perimeter: (35 + 28 + 21) / 2 = 42
And now we just substitute everything into the formula and get
S ^ 2 = 42 * (42-35) * (42-28) * (42-21) = 86436
Then we find the root of 86436 and get 294.
Answer: Triangle area = 294cm