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