While both retinol and Retin-A contain retinoids, they differ in their concentration. Retinol and other forms, such as retinal and retinyl palmitate are found in many over-the-counter anti-aging creams. While these all contain a form of vitamin A, the concentration of retinoids is weak. Retin-A is a prescription retinoid and is a brand name for tretinoin, which is the carboxylic acid form of vitamin A and was one of the early topical acne treatments. Retin-A is sold by prescription because its acid composition is much greater than in over-the-counter products.
Undefined is a term used when a mathematical result has no meaning. More precisely, undefined values occur when an expression is evaluated for input values outside of its domain. ( 1 if no complex numbers). ( 2 if no complex numbers). ( 3 units in radians, no complex infinity). ( 4 if no complex infinity).
Points, Lines and Planes. Points, Lines and Planes are undefined terms in Geometry whose meaning is accepted without definition. These terms have similar meanings in Geometry as they are used in algebra, like the coordinate plane, ordered pairs and lines . Let us see the description of these terms and how they are represented.