Pregunta
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Graph the equation \( y=x^{2}-2 x-8 \) on the accompanying including the roots and the vertex.

Ask by Coleman Coleman. in the United States
Feb 27,2025

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To graph the equation \( y = x^{2} - 2x - 8 \): 1. **Find the Roots**: Solve \( x^{2} - 2x - 8 = 0 \) to get \( x = 4 \) and \( x = -2 \). Plot points (4,0) and (-2,0). 2. **Find the Vertex**: Use \( x = -\frac{b}{2a} = 1 \). Substitute into the equation to find \( y = -9 \). Plot vertex at (1, -9). 3. **Find the y-intercept**: Set \( x = 0 \) to get \( y = -8 \). Plot point (0, -8). 4. **Graph the Parabola**: Draw a symmetric "U" shape with the vertex at (1, -9), passing through the roots and y-intercept. Here's a rough sketch: ``` y ↑ 5 | 4 | 3 | 2 | 1 | 0 —+————•————•————•————→ x | (-2,0) (4,0) -1 | -2 | -3 | -4 | -5 | -6 | -7 | -8 | • (0,-8) -9 | • (1,-9) -10 | | +-------------------------------- -2 -1 0 1 2 3 4 ``` The parabola opens upward, symmetric about the line \( x = 1 \).

Solución

We want to graph the quadratic   y = x² – 2x – 8. Step 1. Find the Roots: To find the x-intercepts, set y = 0:   x² – 2x – 8 = 0. Factor the quadratic:   (x – 4)(x + 2) = 0. So, the roots are:   x – 4 = 0 ⟹ x = 4,   x + 2 = 0 ⟹ x = –2. These give the points (4, 0) and (–2, 0). Step 2. Find the Vertex: For a quadratic in the form y = ax² + bx + c, the x-coordinate of the vertex is given by   x = –b/(2a). Here, a = 1 and b = –2:   x = –(–2)/(2·1) = 2/2 = 1. Now substitute x = 1 into the equation to get y:   y = (1)² – 2(1) – 8 = 1 – 2 – 8 = –9. Thus, the vertex is at (1, –9). Step 3. Find the y-intercept: Set x = 0:   y = 0² – 2·0 – 8 = –8. So, the y-intercept is (0, –8). Step 4. Graphing: 1. Plot the vertex at (1, –9). This is the lowest point on the parabola (since a > 0, the parabola opens upward). 2. Plot the roots (–2, 0) and (4, 0). 3. Plot the y-intercept (0, –8). 4. Draw a smooth curve through these points forming a “U” shape. The parabola is symmetric about the vertical line x = 1. Here is a rough sketch of the graph: y ↑ 5 | 4 | 3 | 2 | 1 | y=0 —+————•————•————•————→ x | (–2,0) (4,0) -1 | -2 | -3 | -4 | -5 | -6 | -7 | -8 | • (0,–8) -9 | • (1,–9) -10 | | +-------------------------------- -2 -1 0 1 2 3 4 Remember, the parabola is symmetric about the vertical line line x = 1. You can plot additional points on both sides of the vertex if needed for accuracy. That is the graph of y = x² – 2x – 8, complete with its roots (–2, 0) and (4, 0) and vertex (1, –9).

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Bonus Knowledge

To graph the equation \( y = x^2 - 2x - 8 \), you can start by finding the roots using the quadratic formula, which reveals that the roots are \( x = 4 \) and \( x = -2 \). Then, find the vertex using the formula \( x = -\frac{b}{2a} \), giving you the vertex at \( (1, -9) \). The graph is a parabola opening upwards, intersecting the y-axis at \( -8 \) and passing through both roots. Another fun tip is to create a table of values; pick several x-values and compute y to plot additional points for a more accurate graph. Common mistakes include not correctly calculating the vertex or roots, so double-check your work with the quadratic formula!

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