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Identify the vertex, axis of symmetry, \( y \) - intercept, \( x \)-intercepts, and opening of the parabola, then sketch the graph. \( y=-2 x^{2}+8 x-5 \)

Ask by Edwards Evans. in the United States
Feb 25,2025

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Answer

The parabola \( y = –2x² + 8x – 5 \) has the following features: - **Vertex**: (2, 3) - **Axis of Symmetry**: x = 2 - **y-intercept**: (0, –5) - **x-intercepts**: Approximately (0.78, 0) and (3.22, 0) - **Opening**: Downward Graph sketch shows the parabola with the vertex at (2,3), y-intercept at (0,–5), and x-intercepts around (0.78,0) and (3.22,0).

Solution

We start with the quadratic function   y = –2x² + 8x – 5 and identify its key features one by one. 1. Vertex:  • The x-coordinate of the vertex is given by –b/(2a). Here a = –2 and b = 8, so   x = –8/(2(–2)) = –8/(–4) = 2.  • To find the y-coordinate, plug x = 2 back into the equation:   y = –2(2)² + 8(2) – 5 = –2(4) + 16 – 5 = –8 + 16 – 5 = 3.  • Thus, the vertex is at (2, 3). 2. Axis of Symmetry:  • The axis of symmetry is the vertical line through the vertex, so   x = 2. 3. y‑Intercept:  • To find the y‑intercept, set x = 0:   y = –2(0)² + 8(0) – 5 = –5.  • Therefore, the y‑intercept is (0, –5). 4. x‑Intercepts:  • To find the x‑intercepts, set y = 0:   –2x² + 8x – 5 = 0.  • Multiply both sides by –1 (to simplify):   2x² – 8x + 5 = 0.  • Use the quadratic formula: x = [8 ± √(64 – 40)]/(2·2) = [8 ± √24]/4.  • Simplify √24: √24 = 2√6, so   x = (8 ± 2√6)/4 = (4 ± √6)/2.  • Thus, the x‑intercepts are at ((4 – √6)/2, 0) and ((4 + √6)/2, 0). 5. Opening:  • The coefficient a = –2 is less than 0, so the parabola opens downward. Graph Sketch: Here’s a rough sketch showing the vertex, intercepts, and axis of symmetry: y ↑ 4 | ● (2,3) Vertex 3 | | 2 | / \ 1 | / \ 0 | -------●---------●-------→ x –1 | / \ –2 | / \ –3 | / \ –4 | / \ –5 | ● (0,–5) (x‑intercepts around 0.78 and 3.22) | +--------------------------------- Notes: • The axis of symmetry is the vertical line x = 2. • The sketch shows the parabola opening downward. • The x‑intercepts (approximately x ≈ 0.78 and x ≈ 3.22) and y‑intercept (0, –5) are roughly plotted. This completes the identification of the key features and the sketch of the parabola.

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The Deep Dive

To find the vertex of the parabola given by the equation \( y = -2x^2 + 8x - 5 \), we can use the vertex formula \( x = -\frac{b}{2a} \). Here, \( a = -2 \) and \( b = 8 \). Plugging in these values gives us \( x = -\frac{8}{2(-2)} = 2 \). To find the y-coordinate of the vertex, substitute \( x = 2 \) back into the equation: \( y = -2(2)^2 + 8(2) - 5 = 3 \). Thus, the vertex is at \( (2, 3) \). The axis of symmetry is the vertical line that passes through the x-coordinate of the vertex, which is \( x = 2 \). To find the \( y \)-intercept, set \( x = 0 \): \( y = -2(0)^2 + 8(0) - 5 = -5 \). Therefore, the \( y \)-intercept is \( (0, -5) \). To find the \( x \)-intercepts, set \( y = 0 \): \[ -2x^2 + 8x - 5 = 0 \rightarrow 2x^2 - 8x + 5 = 0 \rightarrow (x - 1)(x - 2.5) = 0 \] Thus, the \( x \)-intercepts are \( (1, 0) \) and \( (2.5, 0) \). Lastly, the parabola opens downwards since the coefficient of the \( x^2 \) term is negative. Now, sketch the graph with: - Vertex at \( (2, 3) \) - Axis of symmetry as the line \( x = 2 \) - \( y \)-intercept at \( (0, -5) \) - \( x \)-intercepts at \( (1, 0) \) and \( (2.5, 0) \) Get ready for a fabulous parabola party! When you're tackling a quadratic equation like this one, it's kind of like solving a riddle! Always remember to check your \( a \), \( b \), and \( c \) values! A common mistake is forgetting to properly simplify or rearrange the equation, which could lead you to the wrong vertex or intercepts. For those who love puzzles, consider diving deeper into quadratic equations through online courses or math blogs! Websites like Khan Academy or Purplemath offer tons of valuable practice problems and detailed explanations to sharpen your skills and give you confidence in graphing and interpreting these quadratic beauties.

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