Understanding Variables and Expressions
Learn how variables represent unknown quantities in algebraic expressions.
What is a Variable?
A variable is a symbol (usually a letter like x, y, or z) that represents an unknown value or a value that can change.
Examples of variables:
- x could represent an unknown number in an equation
- t might represent time in a physics formula
- r could be the radius of a circle
What is an Algebraic Expression?
An algebraic expression is a combination of variables, numbers, and operations (like addition, subtraction, multiplication, and division).
Examples of algebraic expressions:
- 2x + 3 (a linear expression)
- x² - 4 (a quadratic expression)
- 3x + 2y - z (an expression with multiple variables)
Terms and Coefficients
A term is a part of an expression separated by + or - signs. The coefficient is the number multiplied by the variable in a term.
In the expression 3x² + 5x - 7:
- 3x² is a term with coefficient 3
- 5x is a term with coefficient 5
- -7 is a constant term
Evaluating Expressions
To evaluate an expression means to find its value by substituting specific values for the variables.
Example: Evaluate 2x + 3 when x = 4
2x + 3 = 2(4) + 3
= 8 + 3
= 11