Science, Tech, Math › Math Find Quadratic Line of Symmetry Share Flipboard Email Print Math Pre Algebra & Algebra Math Tutorials Geometry Arithmetic Statistics Exponential Decay Functions Worksheets By Grade Resources View More By Jennifer Ledwith Math Expert B.B.A., Finance and Economics, University of Oklahoma Jennifer Ledwith is the owner of tutoring and test-preparation company Scholar Ready, LLC and a professional writer, covering math-related topics. our editorial process Jennifer Ledwith Updated October 03, 2018 01 of 03 Find Quadratic Line of Symmetry Kelvinsong/Wikimedia Commons/CC0 A parabola is the graph of a quadratic function. Each parabola has a line of symmetry. Also known as the axis of symmetry, this line divides the parabola into mirror images. The line of symmetry is always a vertical line of the form x = n, where n is a real number. This tutorial focuses on how to identify the line of symmetry. Learn how to use either a graph or an equation to find this line. 02 of 03 Find the Line of Symmetry Graphically Jose Camões Silva/Flickr/CC BY 2.0 Find the line of symmetry of y = x2 + 2x with 3 steps. Find the vertex, which is the lowest or highest point of a parabola. Hint: The line of symmetry touches the parabola at the vertex. (-1,-1) What is the x-value of the vertex? -1The line of symmetry is x = -1 Hint: The line of symmetry (for any quadratic function) is always x = n because it is always a vertical line. 03 of 03 Use an Equation to Find the Line of Symmetry F=q(E+v^B)/Wikimedia Commons/CC BY-SA 3.0 The axis of symmetry is also defined by the following equation: x = -b/2a Remember, a quadratic function has the following form: y = ax2 + bx + c Follow 4 steps to use an equation to calculate the line of symmetry for y = x2 + 2x Identify a and b for y = 1x2 + 2x. a = 1; b = 2Plug into the equation x = -b/2a. x = -2/(2*1)Simplify. x = -2/2The line of symmetry is x = -1.