### Constant of Proportionality

The constant value of the ratio of two proportional quantities x and y; usually written y = kx, where k is the constant of proportionality. In a proportional relationship, y = kx, k is the constant of proportionality, which is the value of the ratio between y and x.

### Direct Proportion (Direct Variation)

The relation between two quantities whose ratio remains constant. When one variable increases the other increases proportionally: When one variable doubles the other doubles, when one variable triples the other triples, and so on. When A changes by some factor, then B changes by the same factor: A=kB, where k is the constant of proportionality.

### Division Property of Equality

States that when both sides of an equation are divided by the same number, the remaining expressions are still equal.

### Inverse Operation

A mathematical process that combines two or more numbers such that its product or sum equals the identity.

### Multiplication Property of Equality

States that when both sides of an equation are multiplied by the same number, the remaining expressions are still equal.

### Subtraction Property of Equality

States that when both sides of an equation have the same number subtracted from them, the remaining expressions are still equal.