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The reciprocal function, the function f(x) that maps x to 1/x, is one of the simplest examples of a function which is its own inverse (an involution). Multiplying by a number is the same as dividing by its reciprocal and vice versa. For example, multiplication by 4/5 (or 0.8) will give the same result as division by 5/4 (or 1.25).
[4] It is sometimes denoted RSI-value if the SI (metric) units are used. [5] [12] An R-value can be given for a material (e.g. for polyethylene foam), or for an assembly of materials (e.g. a wall or a window). In the case of materials, it is often expressed in terms of R-value per unit length (e.g. per inch of thickness).
r = | z | = √ x 2 + y 2 is the magnitude of z and; φ = arg z = atan2(y, x). φ is the argument of z, i.e., the angle between the x axis and the vector z measured counterclockwise in radians, which is defined up to addition of 2π. Many texts write φ = tan −1 y / x instead of φ = atan2(y, x), but the first equation needs ...
In some sources, boldface or double brackets x are used for floor, and reversed brackets x or ]x[for ceiling. [7] [8] The fractional part is the sawtooth function, denoted by {x} for real x and defined by the formula {x} = x − ⌊x⌋ [9] For all x, 0 ≤ {x} < 1. These characters are provided in Unicode:
1 (10 0) 1 meter 1 m (exactly) Since 2019, defined as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second, where the second is defined by a hyperfine transition frequency of caesium. 2.72 m Height of Robert Wadlow, tallest-known human. [31] 8.38 m Length of a London bus (AEC Routemaster) 10 1
Functions of the form ae x for constant a are the only functions that are equal to their derivative (by the Picard–Lindelöf theorem). Other ways of saying the same thing include: The slope of the graph at any point is the height of the function at that point. The rate of increase of the function at x is equal to the value of the function at x.
Airtightness improves buildings' energy performance since low airtightness levels imply high infiltration rates, draughts, risk of condensation, and moisture accumulation, and other effects. [12] For this reason, the Passive House standard established performance requirements for airtightness requiring be less than 0.6 ACH with a pressure ...
The Lasance approximation formula is K e /K 0 = 1/(1+C/PP). Some readers might find the notation confusing since the original mK might be interpreted as milliKelvins when it is really meter-Kelvins. He (Lasance?) puts a one (1) at the end of his equation so that it appears like this: K e /K 0 = 1/(1+C/PP)(1).