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Find Quadratic Line of Symmetry

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Use an Equation to Find the Line of Symmetry
Axis 1

Green parabola: y = x^2 + 2x; Red line: Line of Symmetry

Jennifer Ledwith

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

  1. Identify a and b for y = 1x2 + 2x. a = 1; b = 2
  2. Plug into the equation x = -b/2a. x = -2/(2*1)
  3. Simplify. x = -2/2
  4. The line of symmetry is x = -1.
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