What is the equation of the vertical line through x = -7?

• A. x = 0
• B. y = -7
• C. x = -7
• D. x = 7

Answer: (C)

Vertical lines have equations of the form x = constant, since every point on the line shares the same x-coordinate while y can be any value. For the line through x = -7, every point has x = -7, so the equation is x = -7. Graphically, it’s a vertical line crossing the x-axis at -7. The other options describe different lines: x = 0 is the vertical line through the origin, x = 7 is another vertical line parallel to it, and y = -7 is a horizontal line.