Online Math Dictionary: U

Easy to understand math definitions for K-Algebra mathematics
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undefined undefined slope union of sets


If the denominator of a fraction is 0, then the fraction is undefined.

undefined fraction  2/0

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Undefined Slope
Vertical lines have slopes that are called undefined.  This is because, when you try to find the slope given any two points on the line, you always get a zero in the denominator (for the run):

slope = rise / run = rise / 0

For more info on slopes and vertical lines, check out my lessons on lines.

line with an undefined slope

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Union of Sets
The union of two sets is a set of ALL the elements of the two sets.  (You don't write the reruns down twice.)
Example:    A = { 1, 2, 3, a, b, c }     B = { 3, 4, 5, b, c, f, g }
The union is A U B = { 1, 2, 3, 4, 5, a, b, c, f, g }