Sketch it's graph

Mathematics

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Answer

To sketch the graph of y=5−2x−x2y = 5 - 2x - x^2, we will find its key features: the direction of opening, the vertex, the y-intercept, and the x-intercepts.

Step-by-step solution

5 steps
  1. Determine the direction of opening.

    The equation is y=−x2−2x+5y = -x^2 - 2x + 5. Since the coefficient of x2x^2 is −1-1 (which is negative), the parabola opens downwards.

  2. Find the vertex.

    The x-coordinate of the vertex for a parabola y=ax2+bx+cy = ax^2 + bx + c is given by x=−b2ax = -\frac{b}{2a}.
    For y=−x2−2x+5y = -x^2 - 2x + 5, we have a=−1a=-1 and b=−2b=-2.

    x=−−22(−1)=−−2−2=−1x = -\frac{-2}{2(-1)} = -\frac{-2}{-2} = -1

    Now, substitute x=−1x=-1 into the equation to find the y-coordinate:

    y=5−2(−1)−(−1)2y = 5 - 2(-1) - (-1)^2 y=5+2−1y = 5 + 2 - 1 y=6y = 6

    The vertex is at (−1,6)(-1, 6).

  3. Find the y-intercept.

    Set x=0x=0 in the equation:

    y=5−2(0)−(0)2y = 5 - 2(0) - (0)^2 y=5y = 5

    The y-intercept is at (0,5)(0, 5).

  4. Find the x-intercepts (roots).

    Set y=0y=0 in the equation:

    0=5−2x−x20 = 5 - 2x - x^2

    Rearrange to x2+2x−5=0x^2 + 2x - 5 = 0.
    Use the quadratic formula x=−b±b2−4ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}:

    x=−2±22−4(1)(−5)2(1)x = \frac{-2 \pm \sqrt{2^2 - 4(1)(-5)}}{2(1)} x=−2±4+202x = \frac{-2 \pm \sqrt{4 + 20}}{2} x=−2±242x = \frac{-2 \pm \sqrt{24}}{2} x=−2±262x = \frac{-2 \pm 2\sqrt{6}}{2} x=−1±6x = -1 \pm \sqrt{6}

    The x-intercepts are approximately x1=−1+6≈−1+2.45=1.45x_1 = -1 + \sqrt{6} \approx -1 + 2.45 = 1.45 and x2=−1−6≈−1−2.45=−3.45x_2 = -1 - \sqrt{6} \approx -1 - 2.45 = -3.45.
    So, the x-intercepts are approximately (1.45,0)(1.45, 0) and (−3.45,0)(-3.45, 0).

  5. Sketch the graph.

    Plot the vertex (−1,6)(-1, 6), the y-intercept (0,5)(0, 5), and the x-intercepts (−1+6,0)(-1+\sqrt{6}, 0) and (−1−6,0)(-1-\sqrt{6}, 0). Draw a smooth parabolic curve opening downwards through these points.

    Summary of key points for sketching:

    • Opens downwards.
    • Vertex: (−1,6)(-1, 6)
    • Y-intercept: (0,5)(0, 5)
    • X-intercepts: (−1+6,0)(-1+\sqrt{6}, 0) and (−1−6,0)(-1-\sqrt{6}, 0) (approximately (1.45,0)(1.45, 0) and (−3.45,0)(-3.45, 0))
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