What is the area of an isosceles triangle if its base is 120 m and its lateral side is 100 m?

Let us introduce the designations: base a = 120 m, lateral side b = 100 m. The area of an isosceles triangle will be found by the formula:
S = 1/2 * a * h.
We find the height from a right-angled triangle, where we know the hypotenuse (side) and leg (half of the base).
H = √ (b² – (a / 2) ²) = √ (10000 – 3600) = √6400 = 80 (m).
All the data is there, we find the area:
S = 1/2 * a * h = 1/2 * 120 * 80 = 4800 (m²).
Answer: the area is 4800 m².