There are four different triangles with different properties. A scalene triangle has 3 sides of different lengths and 3 unequal angles. An isosceles triangle has 2 sides of equal length.

Letter Published: 02 April 1914 A Triangle that gives the Area and Circumference of any Circle, and the Diameter of a Circle equal in Area to any given Square G. B. MATHEWS Nature 93, 110 (1914 ...