Value
The amount a number, expression or object is worth. In 352, the digit 5 has a value of 50.
Variable
A letter or symbol, such as x or n, that stands for an unknown number or for a quantity that can change.
Variable expression
An expression that contains at least one variable, such as 4x + 1; also called an algebraic expression.
Variance
A measure of spread: the average of the squared distances of the data values from the mean. Its square root is the standard deviation.
Variation
A relationship that describes how one quantity changes with another. In direct variation, y = kx; in inverse variation, y = k/x.
Vector
A quantity with both size (magnitude) and direction, drawn as an arrow. Velocity and force are vectors.
Velocity
The speed of an object in a given direction, such as 60 km/h east. Unlike speed, velocity is a vector.
Venn diagram
A diagram of overlapping circles that shows how sets are related. The overlap holds the elements the sets share.
Verify
To check that an answer is correct, for example by substituting a solution back into the original equation.
Vertex
The point where two rays meet to form an angle, or a corner where the sides of a polygon or the edges of a solid meet.
Vertex angle
The angle formed by the two equal sides of an isosceles triangle. It is opposite the base.
Vertex form
A way of writing a quadratic function, y = a(x − h)² + k, that shows its vertex (h, k) directly.
Vertex of a parabola
The turning point of a parabola: its lowest point when it opens up, or its highest point when it opens down. The axis of symmetry passes through it.
Vertical
Going straight up and down, at a right angle to the horizon. A vertical line is parallel to the y-axis.
Vertical angles
The pair of opposite angles formed when two lines cross. Vertical angles are always equal; they are also called vertically opposite angles.
Vertical asymptote
A vertical line x = a that a graph gets closer and closer to but never touches, often where a denominator equals zero.
Vertical axis
The up-and-down number line on a coordinate plane, usually called the y-axis.
Vertical bar graph
A bar graph whose bars rise straight up from the horizontal axis. The height of each bar shows its value.
Vertical line
A line that goes straight up and down. Its equation is x = a, and its slope is undefined.
Vertical line test
A graph shows a function only if no vertical line crosses it more than once.
Vertical reflection
Flipping a graph over the x-axis. The graph of y = −f(x) is the mirror image of y = f(x).
Vertical shift
Moving a graph straight up or down. The graph of y = f(x) + k is the graph of f moved k units up.
Vertical stretch and compression
Multiplying a function by a number a, as in y = a·f(x). If a > 1 the graph is stretched taller; if 0 < a < 1 it is compressed flatter.
Vertices
The plural of vertex. A cube has 8 vertices, 12 edges and 6 faces.
Vigesimal system
A number system with base 20, used by the ancient Maya. Each place is worth 20 times the place to its right.
Vinculum
A horizontal bar used in math notation, such as the fraction bar, the bar over repeating digits, or the top of a square root sign.
Volume
The amount of space a solid figure takes up or a container can hold, measured in cubic units such as cm³.
Voluntary response sample
A sample made up of people who choose to respond, such as an online poll. It is usually biased, because people with strong opinions are more likely to answer.