In Euclidean geometry the sum of the angles of a triangle is equal to two right angles (180Â°). If all three angles of a triangle are equal, the triangle is called equilateral. An isosceles triangle has two equal angles. A scalene triangle is one in which all three angles are different.
A period, or menstruation, is the shedding of the endometrium-the uterine lining. Menstruation is also known as menses. All female humans, as well as some other female mammals, have regular periods during their reproductive age. Menstruation which includes bleeding from the vagina is found mainly among humans and similar animals, such as primates.
So, the chart below gives the events and their ranges. The average age for periods in the U.S. is 12.16 for black girls and 12.88 for whites. By age 11, 28% of black girls and 13.5% of whites menstruate. By age 12, 62% of blacks, and 35% of whites. A girl's first menstruation is called menarche.