• ### Acute Angle

An angle with a measure of less than 90 degrees.

• ### Addition Properties of Inequality

If a < b, then a + c < b + c
If a > b, then a + c > b + c

• ### Greater Than

a > b if and only if there is a positive number c such that a - c = b.

• ### Inequality

A statement that shows the relationship between two (or more) expressions with one of the following five signs: <, , >, , .

• ### Inequality Properties of Opposites

If a > 0, then - a < 0
If a < 0, then - a > 0

• ### Less Than

a < b if and only if there is a positive number c such that a + c = b.

• ### Multiplication and Division Properties of Inequality

For positive numbers:
If a < b and c > 0, then ac < bc and <
If a > b and c > 0, then ac > bc and >
For negative numbers:
If a < b and c < 0, then ac > bc and >
If a > b and c < 0, then ac < bc and <

• ### Obtuse Angle

An angle with a measure greater than 90 degrees, but not more than 180 degrees.

• ### Property of Squares of Real Numbers

a2≥ 0 for all real numbers a.

• ### Right Angle

An angle with a measure of exactly 90 degrees.

• ### Subtraction Properties of Inequality

If a < b, then a - c < b - c
If a > b, then a - c > b - c

• ### Transitive Properties of Inequality

If a < b and b < c, then a < c.
If a > b and b > c, then a > c.

• ### Trichotomy Property

For any two real numbers a and b, exactly one of the following is true: a < b, a = b, a > b.