Calculate the perimeter of an equilateral triangle if its side length is 25 millimeters.

To calculate the perimeter of a triangle, use the formula:

P = a + b + c,

where P is the perimeter of the triangle,

a, b, c – sides of the triangle.

In our case, the formula will take the form:

P = AB + AC + BC.

Considering that the triangle is equilateral, then its sides are equal: AB = AC = BC.

Therefore, the formula for finding the perimeter of an equilateral triangle can be represented as:

P = AB + BC + AC = 3 * AB = 3 * BC = 3 * AC.

Substitute the values and define the perimeter:

P = 3 * 25mm = 75mm.

Answer: P = 75 mm.