I Identity A statement that is always true. The equations 5 = 5, 7 + 4 = 7 + 4, and x + 8 = x + 8 are examples of identities. Identity property for addition For any real number a, a + 0 = a = 0 + a. Identity property for multiplication For any real number a, a(1) = a = 1(a). Imaginary number i, defined as . Improper fraction A fraction in which the numerator is greater than or equal to the denominator. The fractions are all improper fractions. Inch The smallest unit of length in the American system. 12 inches = 1 foot. Inconsistent equation An equation that has no solution. Inconsistent system of equations A system of equations that does not have a solution. Inconsistent system of linear equations A system of linear equations that has no solution. Independent equations Two equations that are not dependent are said to be independent. Index of a radical Indicates what type of a root is being taken. The index of a cube root is 3. In , the 3 is the index of the radical. In , the index is 4. The index of a square root is 2, but the index is not written in the square root symbol, as shown: Inequality A mathematical statement expressing an order relationship. The following are inequalities: Inequality symbols The symbol that is used to indicate whether a number is greater than another number or less than another number. Since 5 is greater than 3, we would write this with a "greater than" symbol as follows 5 > 3 The statement "7 is less than 12" would be written as follows: 7 < 12. Infinite set A set that has no end to the number of elements that are within it. An infinite set is often indicated by placing an ellipsis (...) after listing some of the elements of the set. Integers The numbers in the infinite set. Intercepts of an equation The point or points where the graph of the equation crosses the x-axis or the y-axis or both. (See x-intercept.) Interest The money that is paid for the use of money. If you deposit money in a bank, the bank uses that money and pays you interest. If you borrow money, you pay the bank interest for the use of that money. Simple interest is determined by the formula I = P x R x T. Compound interest is usually determined by a table, a calculator, or a computer. Intersection of sets The intersection of set A and set B, A B, is the set of elements that belongs to both set A and setB. Inverse function If ƒ(x) is a one-to-one function with ordered pairs of the form, (x , y), its inverse function, (x), will be a one-to-one function with ordered pairs of the form (y, x). Inverse function of a one-to-one function That function obtained by interchanging the first and second coordinates in each ordered pair of the function. . Inverse property of addition For any real number a, a + (-a) = 0 = (-a) + a. Inverse property of multiplication For any real number . Inverse variation When a variable y varies inversely with x, written , where k is the constant of variation. Invert a fraction To invert a fraction is to interchange the numerator and the denominator. If we invert , we obtain the fraction . To invert a fraction is sometimes referred to as to take the reciprocal of a fraction. Irrational numbers Numbers whose decimal forms are nonterminating and nonrepeating. The numbers ...are irrational numbers. Irreducible A fraction that cannot be reduced (simplified) is called irreducible. Isoceles triangle A triangle with two sides equal.

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