To round off a square to 100cm square, one quarter of that area is 25cm square, (10cmx10cm =100/(div)25%=25cm), the area of a right angle triangle with sides measuring ~7.0710cm, equals ~25% of 100cm square, 25cm square of area, (7.0710/2=3.5355 x7.0710=24.9995205).
7.5937 if it is an equilateral triangle.
it is a standard size i use, a handy measurement if you use templates for construction because it in some way represents a metric increment,
(the formula i used is half the base times the height, unless im mistaken i recall that is the correct formula? though i am not a full time mathamatician. for the equalateral triangle i used a web based polygon area calculator.)