i: the basic unit for the imaginary number: i2 = -1.
icosohedron: a polyhedron with 20 faces.
identity: an equation that is true for all values of the variable.
identity element: If * is an operator, then the identity element, I, for * is the number such
that I * a = a. The identity for addition is zero, and the identity for
multiplication is 1.
identity matrix: a square matrix with ones along the diagonal and zeros everywhere else.
If I is an identity matrix, then IA = A.
imaginary number: a number of the form ni, where n is a real number, and i2 = -1.
implication: a conditional statement.
improper fraction: a fraction with a numerator that is greater than the denominator.
incenter: the center of a circle that is inscribed in a triangle. The intersection of the
angle bisectors of the triangle.
incircle: the circle that can be inscribed in a triangle.
increasing function: a function is increasing if f(a) > f(b) when a > b.
increment: a small change, usually indicated by the greek letter delta.
indefinite integral: the sum of the antiderivative of a function and an arbitrary constant.
independent variable: the input number to a function.
infinity: a limitless quantity.
inflection point: a point on a curve such that the curve
is concave up on one side of the
point, and concave down on the other side of the point.
inscribed polygon: a polygon placed inside a circle so
that each vertex of the polygon
touches the circle.
integers: the set of numbers containing zero, the natural
numbers, and all the negatives of
the natural numbers.
integral: If dF(x)/dx = f(x), then F(x) is an integral of f(x). The area under the curve of a
function above the x - axis.
integrand: a function that is to be integrated.
integration: the process of finding an integral.
intercept: the x-intercept of a curve is the point
where the curve crosses the x - axis, and
the y - intercept of a curve is the point where the curve crosses the y - axis.
inversely proportional: y is inversely proportional to x if y = k/x.
irrational number: a number that cannot be expressed as the ratio of two integers.
isometry: a transformation of a figure that does not change
the distances of any two
points in the figure.
isosceles triangle: a triangle with at least two equal sides.
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