I

*i: *the basic unit for the imaginary number: *i*^{2}
= -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 i^{2} = -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.**