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To sketch the graphs of f(x) = x2 − 4 and g(x) = -2x - 4:

Mathematics

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Answer

x = 0 or x = -2\text{x = 0 or x = -2}

-2 < x < 2\text{-2 < x < 2}

Step-by-step solution

6 steps

7.1) To sketch the graphs of f(x)=x2−4f(x) = x^2 - 4 and g(x)=−2x−4g(x) = -2x - 4:

For f(x)=x2−4f(x) = x^2 - 4 (parabola):

  • Shape: Opens upwards.
  • y-intercept: Set x=0  ⟹  f(0)=02−4=−4x=0 \implies f(0) = 0^2 - 4 = -4. Point: (0,−4)(0, -4).
  • x-intercepts: Set f(x)=0  ⟹  x2−4=0  ⟹  (x−2)(x+2)=0  ⟹  x=2f(x)=0 \implies x^2 - 4 = 0 \implies (x-2)(x+2) = 0 \implies x = 2 or x=−2x = -2. Points: (2,0)(2, 0) and (−2,0)(-2, 0).
  • Turning point: For f(x)=ax2+bx+cf(x) = ax^2 + bx + c, the x-coordinate of the turning point is x=−b2ax = \frac{-b}{2a}. Here, a=1,b=0a=1, b=0, so x=02(1)=0x = \frac{0}{2(1)} = 0. The y-coordinate is f(0)=−4f(0) = -4. Point: (0,−4)(0, -4).

For g(x)=−2x−4g(x) = -2x - 4 (straight line):

  • y-intercept: Set x=0  ⟹  g(0)=−2(0)−4=−4x=0 \implies g(0) = -2(0) - 4 = -4. Point: (0,−4)(0, -4).
  • x-intercept: Set g(x)=0  ⟹  −2x−4=0  ⟹  −2x=4  ⟹  x=−2g(x)=0 \implies -2x - 4 = 0 \implies -2x = 4 \implies x = -2. Point: (−2,0)(-2, 0).

Sketching instructions:
Draw a Cartesian plane with x and y axes.

  1. Plot the points (0,−4)(0, -4), (2,0)(2, 0), and (−2,0)(-2, 0) for f(x)f(x). Draw a smooth parabola passing through these points, opening upwards, with (0,−4)(0, -4) as its minimum turning point.
  2. Plot the points (0,−4)(0, -4) and (−2,0)(-2, 0) for g(x)g(x). Draw a straight line passing through these two points. Notice that both graphs intersect at (0,−4)(0, -4) and (−2,0)(-2, 0).

7.2) Use your graphs to determine the values of x if:

7.2.1) f(x)=g(x)f(x) = g(x)
This occurs at the intersection points of the two graphs.

  1. Set the equations equal to each other.

    x2−4=−2x−4x^2 - 4 = -2x - 4
  2. Rearrange the equation to solve for xx.

    x2+2x=0x^2 + 2x = 0
  3. Factor out xx.

    x(x+2)=0x(x+2) = 0
  4. Solve for xx.

    x=0orx=−2x = 0 \quad \text{or} \quad x = -2

    The values of xx where f(x)=g(x)f(x) = g(x) are x = 0 or x = -2\boxed{\text{x = 0 or x = -2}}.

    7.2.2) f(x)<0f(x) < 0
    This means finding the x-values where the graph of f(x)f(x) is below the x-axis.

  5. Identify the x-intercepts of f(x)f(x), which are x=−2x = -2 and x=2x = 2.

  6. Since the parabola f(x)=x2−4f(x) = x^2 - 4 opens upwards, it is below the x-axis between its x-intercepts.

    The values of xx where f(x)<0f(x) < 0 are -2 < x < 2\boxed{\text{-2 < x < 2}}.

    7.3) How can you use the graph of gg to obtain the graph of k(x)=−2x+3k(x) = -2x + 3?
    Given g(x)=−2x−4g(x) = -2x - 4.
    To obtain k(x)=−2x+3k(x) = -2x + 3 from g(x)g(x), we compare the two functions:

    k(x)=−2x+3k(x) = -2x + 3 g(x)=−2x−4g(x) = -2x - 4

    We can see that k(x)=g(x)+7k(x) = g(x) + 7, because −2x−4+7=−2x+3-2x - 4 + 7 = -2x + 3.
    Therefore, you can obtain the graph of k(x)k(x) by shifting the graph of g(x)g(x) vertically upwards by 7 units.

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