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Example 2 - Vertex Formula

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a) y = 2x^2+4x 
    1. we get the a, b, c in the formula y = ax^2 + bx + c
      • a = 2
      • b = 4
      • c = 0
    2. then we plug in a, b into the formula
      • x = -b / (2a)
      • x = -4 / (2*2) = -4/4 = -1
  • so the axis of symmetry is x = -1
  • to find the vertex
  • so the known vertex data is  (-1, y)
  • to find y for the vertex we need to plug -1 into the formula y = 2x^2+4x 
  • y = 2*-1^2+4*-1 = -6
  • so the vertex is (-1, -6)
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B) y = -x^2 + 4x - 5 
    1. we get the a, b, c in the formula y = ax^2 + bx + c
      • a = -1
      • b = 4
      • c = -5
    2. then we plug in a, b into the formula
      • x = -b / (2a)
      • x = -4 / (2*-1) = -4/-2 = 2
  • so the axis of symmetry is x = 2
  • to find the vertex
  • so the known vertex data is  (2, y)
  • to find y for the vertex we need to plug -1 into the formula y = 2x^2+4x 
  • y = -2^2 + 4 * 2 - 5 = -1
  • so the vertex is (2, -1)