What does a linear equation contain?

A linear equation is defined as an equation that represents a straight line when graphed. For an equation to be classified as linear, it must involve at least one variable and cannot include any variable raised to an exponent greater than one. This means that in a linear equation, the variables can only appear to the first power and constants can be included, allowing for addition, subtraction, multiplication by constants, but not exponentiation beyond one or multiplication of variables.

This aligns precisely with the characteristics outlined in the correct answer, which states that a linear equation contains at least one variable and no exponents greater than one. Therefore, such equations take the general form of ( ax + b = 0 ) (where ( a ) and ( b ) are real numbers, and ( x ) is the variable), ensuring that the relationship between the variables remains linear.