Example 2 -Vertex Formula

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)

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