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The figure below shows part of the curve whose equation is given by y = (6−x)(x+2) and the line y = mx + c. (a) Find the coordinates of the point A and B. (b) Determine the equation of the straight line y = mx + c. (c) Find the area between the curve y = (6−x)(x+2) and the line y = mx + c.

Mathematics

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Answers

3 parts
a

A(0,12) and B(6,0)A(0, 12) \text{ and } B(6, 0)

b

y=−2x+12y = -2x + 12

c

36 units236 \text{ units}^2

Step-by-step solution

7 steps

Part a· 2 steps

To find the coordinates of points A and B

Point A is the y-intercept of the curve y=(6−x)(x+2)y = (6-x)(x+2). This occurs when x=0x=0.
Point B is the x-intercept of the curve y=(6−x)(x+2)y = (6-x)(x+2). This occurs when y=0y=0.

  1. Find the coordinates of A.

    Substitute x=0x=0 into the curve equation:

    y=(6−0)(0+2)=6×2=12y = (6-0)(0+2) = 6 \times 2 = 12

    So, the coordinates of A are (0,12)(0, 12).

  2. Find the coordinates of B.

    Set y=0y=0 in the curve equation:

    (6−x)(x+2)=0(6-x)(x+2) = 0

    This gives two possible x-values: 6−x=0  ⟹  x=66-x=0 \implies x=6 or x+2=0  ⟹  x=−2x+2=0 \implies x=-2.
    From the graph, point B is the positive x-intercept.
    So, the coordinates of B are (6,0)(6, 0).
    The coordinates of A and B are A(0,12) and B(6,0)\boxed{A(0, 12) \text{ and } B(6, 0)}.

Part b

y=−2x+12y = -2x + 12

To determine the equation of the straight line y=mx+cy = mx+c

The line passes through points A$(0, 12)$ and B$(6, 0)$.

  1. Find the slope mm.

    The slope mm is given by the formula m=y2−y1x2−x1m = \frac{y_2 - y_1}{x_2 - x_1}.

    m=0−126−0=−126=−2m = \frac{0 - 12}{6 - 0} = \frac{-12}{6} = -2
  2. Find the y-intercept cc.

    Since point A is (0,12)(0, 12), the y-intercept cc is 12.
    Substitute m=−2m=-2 and c=12c=12 into y=mx+cy=mx+c.
    The equation of the straight line is y=−2x+12\boxed{y = -2x + 12}.

Part c

36 units236 \text{ units}^2

To find the area between the curve y=(6−x)(x+2)y = (6-x)(x+2) and the line y=mx+cy = mx+c

First, expand the curve equation and use the line equation found in part (b).
The curve is y=(6−x)(x+2)=6x+12−x2−2x=−x2+4x+12y = (6-x)(x+2) = 6x + 12 - x^2 - 2x = -x^2 + 4x + 12.
The line is y=−2x+12y = -2x + 12.
The points of intersection are A (x=0x=0) and B (x=6x=6), which will be the limits of integration.

  1. Set up the integral for the area.

    The area between two curves f(x)f(x) and g(x)g(x) from x=ax=a to x=bx=b is ∫ab(f(x)−g(x)) dx\int_{a}^{b} (f(x) - g(x)) \,dx, where f(x)f(x) is the upper curve.
    Let f(x)=−x2+4x+12f(x) = -x^2 + 4x + 12 (curve) and g(x)=−2x+12g(x) = -2x + 12 (line).
    In the interval [0,6][0, 6], the curve is above the line.
    The difference between the curve and the line is:

    (−x2+4x+12)−(−2x+12)=−x2+4x+12+2x−12=−x2+6x(-x^2 + 4x + 12) - (-2x + 12) = -x^2 + 4x + 12 + 2x - 12 = -x^2 + 6x

    The area is given by the integral:

    Area=∫06(−x2+6x) dx\text{Area} = \int_{0}^{6} (-x^2 + 6x) \,dx
  2. Evaluate the integral.

    Integrate term by term:

    ∫(−x2+6x) dx=−x33+6x22=−x33+3x2\int (-x^2 + 6x) \,dx = -\frac{x^3}{3} + \frac{6x^2}{2} = -\frac{x^3}{3} + 3x^2
  3. Apply the limits of integration.

    Area=[−x33+3x2]06\text{Area} = \left[ -\frac{x^3}{3} + 3x^2 \right]_{0}^{6} Area=(−633+3(62))−(−033+3(02))\text{Area} = \left( -\frac{6^3}{3} + 3(6^2) \right) - \left( -\frac{0^3}{3} + 3(0^2) \right) Area=(−2163+3(36))−(0)\text{Area} = \left( -\frac{216}{3} + 3(36) \right) - (0) Area=(−72+108)\text{Area} = (-72 + 108) Area=36\text{Area} = 36

    The area between the curve and the line is 36 units2\boxed{36 \text{ units}^2}.

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