Ρ

Ro in a capital letter Etymologicum Magnum (1499).

Ro (according to the RAE since 2001) or rho (in capital letters Ρ, lowercase ρ [italics ϱ]; Ancient Greek call ῥῶ rhô /r̥ɔ̂ː/, in modern Greek ρο/ρω ro/rô /ro/) is the seventeenth letter of the Greek alphabet. In ancient Greek, the word-beginning ro was written with a rough spirit (a symbol normally reserved for vowels and representing an aspiration) which in the case of the ro probably represented a multiple trill pronunciation (as in English).. The same testifies that, as in Spanish, in Greek those compound words whose second element begins with this letter are written with a double r. For example: πολύρριζος [po'lyrridzos] "polyrrizos" ("of various roots").

In the Greek numeral system it has a value of 100 (Ρʹ).

History

Epigraphic variants

In archaic epigraphic sources the following variants appear:

Use

In the Greek numeral system it has a value of 100 (ρʹ).

The lowercase letter ρ is used to symbolize:

• In mathematics, radio in polar coordinate system.
• In continuous media mechanics, the density of a material.
• In electricity, the resistance of a material.
• In statistics, the correlation coefficient between two variables, which is defined as the covariance of the variables divided between the product of the corresponding standard deviations.
• In economy, the discount factor associated with a profit or premium to pay for risk aversion.

Unicode

• Greek

• Symbol

• Copt

• Maths