An isosceles triangle has two sides of equal length and a third, different side called the base — the shape you see in classic roof gables and traffic yield signs.
An isosceles triangle has two sides of equal length and a third, different side called the base — the shape you see in classic roof gables and traffic yield signs. This calculator finds the triangle's height, area, and perimeter from the base and the length of the two equal sides.
A gable roof triangle has a base of 8 m and equal sides of 5 m each. Height = √(5² − 4²) = √9 = 3 m. Area = 0.5 × 8 × 3 = 12 m². Perimeter = 2(5) + 8 = 18 m.
Area = 0.5 × base × height; height can be found via the Pythagorean theorem from the base and the two equal sides.
It has exactly two sides of equal length, and correspondingly two equal base angles.
Equilateral has all three sides equal; isosceles has only two equal sides (equilateral is a special case of isosceles).