The vertices of a quadrilateral [tex]A B C D[/tex] are [tex]A(4,0), B(14,11), C(-10,6)[/tex], and [tex]D(-10,-5)[/tex].

(i) Show that [tex]A C[/tex] and [tex]B D[/tex] bisect each other at right angles.

(ii) Calculate the ratio [tex]|B D|:|A C|[/tex].



Answer :

Let's break down the problem into two main parts as requested:

### Part (i): Show that [tex]\(AC\)[/tex] and [tex]\(BD\)[/tex] bisect each other at right angles.

1. Midpoints of [tex]\(AC\)[/tex] and [tex]\(BD\)[/tex]:

- Midpoint of [tex]\(AC\)[/tex]:
To find the midpoint of a line segment between two points [tex]\((x_1, y_1)\)[/tex] and [tex]\((x_2, y_2)\)[/tex], we use:
[tex]\[ \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right) \][/tex]
For [tex]\(A(4, 0)\)[/tex] and [tex]\(C(-10, 6)\)[/tex]:
[tex]\[ \text{Midpoint of } AC = \left( \frac{4 + (-10)}{2}, \frac{0 + 6}{2} \right) = \left( \frac{-6}{2}, \frac{6}{2} \right) = (-3.0, 3.0) \][/tex]

- Midpoint of [tex]\(BD\)[/tex]:
For [tex]\(B(14, 11)\)[/tex] and [tex]\(D(-10, -5)\)[/tex]:
[tex]\[ \text{Midpoint of } BD = \left( \frac{14 + (-10)}{2}, \frac{11 + (-5)}{2} \right) = \left( \frac{4}{2}, \frac{6}{2} \right) = (2.0, 3.0) \][/tex]

The midpoints are [tex]\((-3.0, 3.0)\)[/tex] and [tex]\((2.0, 3.0)\)[/tex], indicating they do not coincide.

Since the midpoints [tex]\(({-3.0, 3.0})\)[/tex] and [tex]\((2.0, 3.0)\)[/tex] are not the same, [tex]\(AC\)[/tex] and [tex]\(BD\)[/tex] do not bisect each other.

2. Slopes of [tex]\(AC\)[/tex] and [tex]\(BD\)[/tex]:

- Slope of [tex]\(AC\)[/tex]:
The slope between two points [tex]\((x_1, y_1)\)[/tex] and [tex]\((x_2, y_2)\)[/tex] is:
[tex]\[ \text{Slope} = \frac{y_2 - y_1}{x_2 - x_1} \][/tex]
For [tex]\(A(4, 0)\)[/tex] and [tex]\(C(-10, 6)\)[/tex]:
[tex]\[ \text{Slope of } AC = \frac{6 - 0}{-10 - 4} = \frac{6}{-14} = -\frac{3}{7} = -0.42857142857142855 \][/tex]

- Slope of [tex]\(BD\)[/tex]:
For [tex]\(B(14, 11)\)[/tex] and [tex]\(D(-10, -5)\)[/tex]:
[tex]\[ \text{Slope of } BD = \frac{-5 - 11}{-10 - 14} = \frac{-16}{-24} = \frac{2}{3} = 0.6666666666666666 \][/tex]

3. Perpendicularity:

The product of the slopes of two perpendicular lines is [tex]\(-1\)[/tex]. Calculate the product of the slopes:
[tex]\[ \text{Product of slopes} = (-0.42857142857142855) \times 0.6666666666666666 \approx -0.2857142857142857 \][/tex]
Since the product is not [tex]\(-1\)[/tex], [tex]\(AC\)[/tex] and [tex]\(BD\)[/tex] are not perpendicular.

### Part (ii): Calculate the ratio [tex]\(|BD| : |AC|\)[/tex].

1. Length of [tex]\(BD\)[/tex]:
The length of a line segment between two points [tex]\((x_1, y_1)\)[/tex] and [tex]\((x_2, y_2)\)[/tex] is:
[tex]\[ \text{Length} = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2} \][/tex]
For [tex]\(B(14, 11)\)[/tex] and [tex]\(D(-10, -5)\)[/tex]:
[tex]\[ \text{Length of } BD = \sqrt{(14 - (-10))^2 + (11 - (-5))^2} = \sqrt{(24)^2 + (16)^2} = \sqrt{576 + 256} = \sqrt{832} \approx 28.844410203711913 \][/tex]

2. Length of [tex]\(AC\)[/tex]:
For [tex]\(A(4, 0)\)[/tex] and [tex]\(C(-10, 6)\)[/tex]:
[tex]\[ \text{Length of } AC = \sqrt{(4 - (-10))^2 + (0 - 6)^2} = \sqrt{(14)^2 + (-6)^2} = \sqrt{196 + 36} = \sqrt{232} \approx 15.231546211727817 \][/tex]

3. Ratio [tex]\(|BD| : |AC|\)[/tex]:
[tex]\[ \text{Ratio} = \frac{|BD|}{|AC|} = \frac{28.844410203711913}{15.231546211727817} \approx 1.8937283058959973 \][/tex]

### Summary:
- [tex]\(AC\)[/tex] and [tex]\(BD\)[/tex] do not bisect each other.
- [tex]\(AC\)[/tex] and [tex]\(BD\)[/tex] are not perpendicular.
- The ratio [tex]\(|BD| : |AC|\)[/tex] is approximately [tex]\(1.8937\)[/tex].

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