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Graphing Quadratic Functions in Standard Form y = ax 2 + bx + c

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Quadratic Functions The graph of a quadratic function is a parabola. A parabola can open up or down. If the parabola opens up, the lowest point (minimum) is called the vertex. If the parabola opens down, the vertex is the highest point (maximum). NOTE: if the parabola opened left or right it would not be a function! Vertex (Minimum) Vertex (Maximum)

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y = ax 2 + bx + c The parabola will open down when the a value is negative. The parabola will open up when the a value is positive. Standard Form The standard form of a quadratic function is a > 0 a < 0

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y x Line of Symmetry Parabolas have a symmetric property to them. If we drew a line down the middle of the parabola, we could fold the parabola in half. We call this line the line of symmetry. The line of symmetry ALWAYS passes through the vertex.

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Find the line of symmetry of y = 3x 2 – 18x + 7 Finding the Line of Symmetry When a quadratic function is in standard form The equation of the line of symmetry is y = ax 2 + bx + c, For example… This is best read as … the opposite of b divided by the quantity of 2 times a.

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Finding the Vertex We know the line of symmetry always goes through the vertex. Thus, the line of symmetry gives us the x – coordinate of the vertex. To find the y – coordinate of the vertex, we need to plug the x – value into the original equation. For example, Find the vertex y = –2x 2 + 8x –3

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A Quadratic Function in Standard Form The standard form of a quadratic function is given by y = ax 2 + bx + c STEP 1: Find the line of symmetry STEP 2: Find the vertex STEP 3: Make a table of values using x values close to the line of symmetry. (Put the vertex in the middle of your table of values.)

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Example 1 a. Graph b.Find and label the axis of symmetry. c.Find the maximum/minimum d.Find the domain & range y = 2x 2 – 4x – 1 A Quadratic Function in Standard Form

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Example 2 a. Graph b.Find and label the axis of symmetry. c.Find the maximum/minimum d.Find the domain & range y = x 2 - 2x – 1

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A Quadratic Function in Standard Form Example 3 a. Graph b.Find and label the axis of symmetry. c.Find the maximum/minimum d.Find the domain & range y = -1/6x 2 – x – 3

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