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The graph of f(x) = 4/(x+2) + 3 is drawn below. C is the point of intersection of the asymptotes of f and B is the x-intercept of f.

Mathematics

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5 parts
6.1

x=−2x=-2

6.2

y∈R,y≠3y \in \mathbb{R}, y \neq 3

6.3

(−103,0)\left(-\frac{10}{3}, 0\right)

6.4

k=−13 or k=3k=-13 \text{ or } k=3

6.5

1323\frac{13\sqrt{2}}{3}

Graph of f(x) = 4/(x + 2) + 3

Use the left and right arrow keys to trace the curve, up and down to jump between key points, and plus and minus to zoom.

Key points of f(x) = 4/(x + 2) + 3
Pointxy
x-intercept−3.330
y-intercept05

Step-by-step solution

14 steps

Here's the solution to Question 6:

The given function is f(x)=4x+2+3f(x) = \frac{4}{x+2} + 3.

Part 6.1· 1 step

Write down the equation of the vertical asymptote of f.

  1. The vertical asymptote occurs where the denominator of the rational part of the function is zero.

    x+2=0x+2 = 0 x=−2x = -2

    The equation of the vertical asymptote is x=−2\boxed{x=-2}.

Part 6.2

y∈R,y≠3y \in \mathbb{R}, y \neq 3

Write down the range of f.

  1. The horizontal asymptote of the function f(x)=ax−p+qf(x) = \frac{a}{x-p} + q is y=qy=q.

    In this case, q=3q=3.
    The range of a hyperbola is all real numbers except the value of its horizontal asymptote.
    The range of ff is y∈R,y≠3\boxed{y \in \mathbb{R}, y \neq 3}.

Part 6.3

(−103,0)\left(-\frac{10}{3}, 0\right)

Calculate the coordinates of B.

  1. B is the x-intercept of ff.

    To find the x-intercept, set f(x)=0f(x)=0.

    0=4x+2+30 = \frac{4}{x+2} + 3
  2. Solve for xx.

    −3=4x+2-3 = \frac{4}{x+2} −3(x+2)=4-3(x+2) = 4 −3x−6=4-3x - 6 = 4 −3x=10-3x = 10 x=−103x = -\frac{10}{3}

    The coordinates of B are (−103,0)\boxed{\left(-\frac{10}{3}, 0\right)}.

Part 6.4

k=−13 or k=3k=-13 \text{ or } k=3

Determine the values of k for which y=−4x+ky=-4x+k is a tangent to f.

  1. Set the function f(x)f(x) equal to the line y=−4x+ky=-4x+k.

    4x+2+3=−4x+k\frac{4}{x+2} + 3 = -4x+k
  2. Multiply both sides by (x+2)(x+2) to eliminate the denominator.

    4+3(x+2)=(−4x+k)(x+2)4 + 3(x+2) = (-4x+k)(x+2) 4+3x+6=−4x2−8x+kx+2k4 + 3x + 6 = -4x^2 - 8x + kx + 2k 3x+10=−4x2+(k−8)x+2k3x + 10 = -4x^2 + (k-8)x + 2k
  3. Rearrange the equation into the standard quadratic form ax2+bx+c=0ax^2+bx+c=0.

    4x2+3x−(k−8)x+10−2k=04x^2 + 3x - (k-8)x + 10 - 2k = 0 4x2+(3−k+8)x+(10−2k)=04x^2 + (3 - k + 8)x + (10 - 2k) = 0 4x2+(11−k)x+(10−2k)=04x^2 + (11 - k)x + (10 - 2k) = 0
  4. For the line to be a tangent, there must be exactly one point of intersection, which means the discriminant (Δ\Delta) of the quadratic equation must be zero.

    Δ=b2−4ac=0\Delta = b^2 - 4ac = 0.
    Here, a=4a=4, b=(11−k)b=(11-k), c=(10−2k)c=(10-2k).

    (11−k)2−4(4)(10−2k)=0(11-k)^2 - 4(4)(10-2k) = 0 (121−22k+k2)−16(10−2k)=0(121 - 22k + k^2) - 16(10-2k) = 0 121−22k+k2−160+32k=0121 - 22k + k^2 - 160 + 32k = 0 k2+10k−39=0k^2 + 10k - 39 = 0
  5. Solve the quadratic equation for kk.

    (k+13)(k−3)=0(k+13)(k-3) = 0 k+13=0ork−3=0k+13=0 \quad \text{or} \quad k-3=0 k=−13ork=3k=-13 \quad \text{or} \quad k=3

    The values of kk are k=−13 or k=3\boxed{k=-13 \text{ or } k=3}.

Part 6.5

1323\frac{13\sqrt{2}}{3}

Calculate the distance between B and D, where D is the reflection of B in the line of symmetry of f, having a negative gradient.

  1. Identify the coordinates of B and the equation of the line of symmetry with a negative gradient.

    From 6.3, B is (−103,0)\left(-\frac{10}{3}, 0\right).
    The point of intersection of the asymptotes (C) is (−2,3)(-2, 3). The lines of symmetry pass through C.
    The general equations for the lines of symmetry of f(x)=ax−p+qf(x) = \frac{a}{x-p} + q are y−q=±(x−p)y-q = \pm(x-p).
    So, y−3=±(x−(−2))y-3 = \pm(x-(-2))
    y−3=±(x+2)y-3 = \pm(x+2)
    The line of symmetry with a negative gradient is y−3=−(x+2)y-3 = -(x+2).

    y=−x−2+3y = -x-2+3 y=−x+1y = -x+1
  2. Find the coordinates of D, the reflection of B in the line y=−x+1y=-x+1.

    Let B be (xB,yB)=(−103,0)(x_B, y_B) = (-\frac{10}{3}, 0) and D be (xD,yD)(x_D, y_D).
    The line segment BD is perpendicular to the line of symmetry y=−x+1y=-x+1. The gradient of the line of symmetry is −1-1, so the gradient of BD is 1.
    The equation of the line passing through B and D is y−yB=1(x−xB)y - y_B = 1(x - x_B).

    y−0=1(x−(−103))y - 0 = 1\left(x - \left(-\frac{10}{3}\right)\right) y=x+103y = x + \frac{10}{3}
  3. Find the midpoint M of BD, which is the intersection of the line BD and the line of symmetry.

    x+103=−x+1x + \frac{10}{3} = -x+1 2x=1−1032x = 1 - \frac{10}{3} 2x=3−1032x = \frac{3-10}{3} 2x=−732x = -\frac{7}{3} xM=−76x_M = -\frac{7}{6}

    Substitute xMx_M into the line of symmetry equation to find yMy_M:

    yM=−(−76)+1y_M = -(-\frac{7}{6}) + 1 yM=76+66y_M = \frac{7}{6} + \frac{6}{6} yM=136y_M = \frac{13}{6}

    So, the midpoint M is (−76,136)\left(-\frac{7}{6}, \frac{13}{6}\right).

  4. Use the midpoint formula to find the coordinates of D.

    xM=xB+xD2  ⟹  −76=−103+xD2x_M = \frac{x_B+x_D}{2} \implies -\frac{7}{6} = \frac{-\frac{10}{3}+x_D}{2} −73=−103+xD-\frac{7}{3} = -\frac{10}{3}+x_D xD=−73+103=33=1x_D = -\frac{7}{3} + \frac{10}{3} = \frac{3}{3} = 1 yM=yB+yD2  ⟹  136=0+yD2y_M = \frac{y_B+y_D}{2} \implies \frac{13}{6} = \frac{0+y_D}{2} yD=133y_D = \frac{13}{3}

    So, D is (1,133)\left(1, \frac{13}{3}\right).

  5. Calculate the distance between B(−103,0)\left(-\frac{10}{3}, 0\right) and D(1,133)\left(1, \frac{13}{3}\right) using the distance formula d=(x2−x1)2+(y2−y1)2d = \sqrt{(x_2-x_1)^2 + (y_2-y_1)^2}.

    dBD=(1−(−103))2+(133−0)2d_{BD} = \sqrt{\left(1 - \left(-\frac{10}{3}\right)\right)^2 + \left(\frac{13}{3} - 0\right)^2} dBD=(33+103)2+(133)2d_{BD} = \sqrt{\left(\frac{3}{3} + \frac{10}{3}\right)^2 + \left(\frac{13}{3}\right)^2} dBD=(133)2+(133)2d_{BD} = \sqrt{\left(\frac{13}{3}\right)^2 + \left(\frac{13}{3}\right)^2} dBD=2⋅(133)2d_{BD} = \sqrt{2 \cdot \left(\frac{13}{3}\right)^2} dBD=1332d_{BD} = \frac{13}{3}\sqrt{2}

    The distance between B and D is 1323\boxed{\frac{13\sqrt{2}}{3}}.

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