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The vertices of a parallelogram are [tex]\( A(x_1, y_1), B(x_2, y_2), C(x_3, y_3), \)[/tex] and [tex]\( D(x_4, y_4) \)[/tex]. Which of the following must be true if parallelogram [tex]\( ABCD \)[/tex] is proven to be a rectangle?

A. [tex]\(\left(\frac{y_4-y_3}{x_4-x_3} = \frac{y_3-y_2}{x_3-x_2}\right)\)[/tex] and [tex]\(\left(\frac{y_4-y_3}{x_4-x_3} \times \frac{y_3-y_2}{x_3-x_2}\right) = -1\)[/tex]

B. [tex]\(\left(\frac{y_4-y_3}{x_4-x_3} = \frac{y_2-y_1}{x_2-x_1}\right)\)[/tex] and [tex]\(\left(\frac{y_4-y_3}{x_4-x_3} \times \frac{y_2-y_1}{x_2-x_1}\right) = -1\)[/tex]

C. [tex]\(\left(\frac{y_4-y_3}{x_4-x_3} = \frac{y_2-y_1}{x_2-x_1}\right)\)[/tex] and [tex]\(\left(\frac{y_4-y_3}{x_4-x_3} \times \frac{y_3-y_2}{x_3-x_2}\right) = -1\)[/tex]

D. [tex]\(\left(\frac{y_4-y_3}{x_4-x_3} = \frac{y_3-y_1}{x_3-x_1}\right)\)[/tex] and [tex]\(\left(\frac{y_4-y_3}{x_4-x_3} \times \frac{y_2-y_1}{x_2-x_1}\right) = -1\)[/tex]


Sagot :

To determine if a parallelogram [tex]\(ABCD\)[/tex] is a rectangle, we need to examine the properties of its sides and angles. Specifically, in addition to the condition that opposite sides are parallel (which is inherent in any parallelogram), a rectangle requires that adjacent sides are perpendicular to each other. This perpendicularity criterion is mathematically determined by the slopes of the sides.

1. Parallelism of Opposite Sides:
The slopes of opposite sides must be equal for the parallelogram to hold its shape:
[tex]\[ \text{Slope of } AB = \text{Slope of } CD \quad \text{and} \quad \text{Slope of } BC = \text{Slope of } DA. \][/tex]

2. Perpendicularity of Adjacent Sides:
The product of the slopes of two perpendicular lines is [tex]\(-1\)[/tex]. Therefore, the product of the slopes of adjacent sides must be [tex]\(-1\)[/tex].

Let's analyze the options given:

- Option A:
[tex]\[ \left(\frac{y_4-y_3}{x_4-x_3}=\frac{y_3-y_2}{x_3-x_2}\right) \quad \text{and} \quad \left(\frac{y_4-y_3}{x_4-x_3} \times \frac{y_3-y_2}{x_3-x_2}\right)=-1 \][/tex]
This suggests checking the slope of [tex]\(CD\)[/tex] equals the slope of [tex]\(BC\)[/tex] (parallelism), and then verifying they are perpendicular, which doesn't check all adjacent pairs required.

- Option B:
[tex]\[ \left(\frac{y_4-y_3}{x_4-x_3}=\frac{y_2-y_1}{x_2-x_1}\right) \quad \text{and} \quad \left(\frac{y_4-y_3}{x_4-x_3} \times \frac{y_2-y_1}{x_2-x_1}\right)=-1 \][/tex]
This correctly examines if opposite sides (like [tex]\(CD\)[/tex] and [tex]\(AB\)[/tex]) are parallel, and checks if the slopes of [tex]\(CD\)[/tex] and [tex]\(AB\)[/tex] (or any appropriate adjacent sides pair) multiply to [tex]\(-1\)[/tex], ensuring perpendicularity.

- Option C:
[tex]\[ \left(\frac{y_4-y_3}{x_4-x_3}=\frac{y_2-y_1}{x_2-x_1}\right) \quad \text{and} \quad \left(\frac{y_4-y_3}{x_4-x_3} \times \frac{y_3-y_2}{x_3-x_2}\right)=-1 \][/tex]
This closely resembles option B but it incorrectly places perpendicularity check involving non-adjacent slopes.

- Option D:
[tex]\[ \left(\frac{y_4-y_3}{x_4-x_3}=\frac{y_3-y_1}{x_3-x_1}\right) \quad \text{and} \quad \left(\frac{y_4-y_3}{x_4-x_3} \times \frac{y_2-y_1}{x_2-x_1}\right)=-1 \][/tex]
This would imply testing slopes involving different vertices' connections and does not symmetrically validate adjacency/pairing needed for parallelogram sides correctly.

Hence, option B ensures parallelism and perpendicularity in the correct adjacent pairings context verifying [tex]\(ABCD\)[/tex] being a rectangle:
[tex]\[ \left(\frac{y_4-y_3}{x_4-x_3} = \frac{y_2-y_1}{x_2-x_1}\right) \quad \text{and} \quad \left(\frac{y_4-y_3}{x_4-x_3} \times \frac{y_2-y_1}{x_2-x_1}\right) = -1. \][/tex]

Therefore, the correct answer is:
[tex]\[ \boxed{2} \][/tex]