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Snell's law is the simple formula used to calculate the refraction of light when travelling between two media of differing refractive index. It is named after one of its discoverers, Dutch mathematician Willebrord van Roijen Snell (1580–1626).
[14] [15] It is said to be an improper fraction, or sometimes top-heavy fraction, [16] if the absolute value of the fraction is greater than or equal to 1. Examples of proper fractions are 2/3, −3/4, and 4/9, whereas examples of improper fractions are 9/4, −4/3, and 3/3.
In statistics, the 68–95–99.7 rule, also known as the empirical rule, and sometimes abbreviated 3sr or 3 σ, is a shorthand used to remember the percentage of values that lie within an interval estimate in a normal distribution: approximately 68%, 95%, and 99.7% of the values lie within one, two, and three standard deviations of the mean ...
In the 3rd century BCE, Archimedes proved the sharp inequalities 223 ⁄ 71 < π < 22 ⁄ 7, by means of regular 96-gons (accuracies of 2·10 −4 and 4·10 −4, respectively). [ 15 ] In the 2nd century CE, Ptolemy used the value 377 ⁄ 120 , the first known approximation accurate to three decimal places (accuracy 2·10 −5 ). [ 16 ]
The number π (/ p aɪ / ⓘ; spelled out as "pi") is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle's circumference to its diameter.It appears in many formulae across mathematics and physics, and some of these formulae are commonly used for defining π, to avoid relying on the definition of the length of a curve.
Brix measurements are also used in the dairy industry to measure the quality of colostrum given to newborn calves, goats, and sheep. [8] Modern optical Brix meters are divided into two categories. In the first are the Abbe-based instruments in which a drop of the sample solution is placed on a prism; the result is observed through an eyepiece.
Passive solar fraction (PSF) is the percentage of the required heat load met by PSH and hence represents potential reduction in heating costs. RETScreen International has reported a PSF of 20–50%. Within the field of sustainability, energy conservation even of the order of 15% is considered substantial. Other sources report the following PSFs: