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Cross Product
Given two nonzero vectors in two or three dimensions, their cross product is a vector with magnitude equal to the product of the magnitudes of the vectors times the sine of the angle between the vectors and direction perpendicular to the vectors.
5079#5291
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Definition Limit ⪢⪢
Let f:A→R be a function whose domain A contains the interval [a,∞) for some fixed real value of a. Then f(x) tends to L as x tends to infinity, if for every ε>0 there exists a real number X such that
x>X ⇒ ⎹f(x)−L⎸<ε.
5079#4818
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limit⎾f(x)⏐x→∞⏌= L ⪢⪢
Let f:A→R be a function whose domain A contains the interval [a,∞) for some fixed real value of a. Then f(x) tends to L as x tends to infinity, if for every ε>0 there exists a real number X such that
x>X ⇒ ⎹f(x)−L⎸<ε.
5079#3473
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Sandwich rule ⪢⪢
Let f, g and h be functions such that f(x)≤g(x)≤h(x) for all x in some neighborhood of c and such that f(c)=g(c)=h(c).
If f and h are conyinuous at c, then so is g.
5079#6899
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Sum/product/reciprocal rules ⪢⪢
Sum rule. If f and g are continuous at c then f+g is continuous at c.┆Product rule. If f and g are continuous at c then f·g is continuous at c.┆Reciprocal rule. If f is continuous at c and f(c) is not 0 then 1/f is continuous at c.
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Φ ≈ 1.618 ⪢⪢
Keplar observed that the relationship between a number in the Fibonacci sequence and the previous number more and more closely approaches the irrational number Φ, the longer the sequence is continued. #math #bookmark
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