Vocabulary

Variable: A symbol, usually a letter, used to represent a number in mathematical expressions or sentences.

Equation: An equation is a mathematical sentence stating that two quantities are equal. ​

Linear Equation: An equation with a graph that is a straight line.

Concept

Solve linear equations in the form y = ax or y = mx + b by substitution.

Rules

1. Substitute the variable in the equation with its given value. 
2. Follow the order of operations to simplify. 

Example

If y = 3x - 7, find the value of y when x = 9. 

Solution

Substitute 9 for x in the equation: 

y = 3x - 7

y = 3(9) - 7 

y = 27 - 7

y = 20

Pre-requisite Skills

Solve Multi-Step Equations (8.2.5)

Solve Two-Step Equations (8.2.2)

Solve Equations with Rational Coefficients (8.2.1)