Which form represents a one-variable linear equation?

• A. ax + b = 0
• B. ax^2 + b = 0
• C. ax + b = c
• D. x = a + b

Answer: (A)

A one-variable linear equation uses a single variable, and that variable appears to the first power with no other variable terms. Writing it in the standard form a times the variable plus a constant equals zero makes the linear relationship explicit and the solution straightforward: x equals negative b over a, provided a is not zero.

The form ax^2 + b = 0 isn’t linear because the x term is squared, which makes it a quadratic. The form ax + b = c is still linear in one variable and can be rearranged to the standard form ax + b = 0, but the canonical representation often presented is ax + b = 0, which is why that option is the typical example of a one-variable linear equation.