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Use your knowledge of the slopes of parallel and perpendicular lines. Is the figure with vertices at \((-11,-5),(-2,-19),(12,-10),\) and \((3,4)\) a parallelogram? Is it a rectangle? (Hint: A rectangle is a parallelogram with a right angle.)

Short Answer

Expert verified
The figure is a rectangle because it is a parallelogram with perpendicular adjacent sides.

Step by step solution

01

Find the Slopes of Opposite Sides

First, calculate the slopes of the sides formed by the vertices. Use the slope formula \(\text{slope} = \frac{y_2 - y_1}{x_2 - x_1}\). Calculate the slopes for each pair of points: \((-11, -5)\) to \((-2, -19)\), \((-2, -19)\) to \(12, -10)\), \(12, -10)\) to \(3, 4)\), and \(3, 4)\) to \((-11, -5)\).
02

Calculate Slope for Side 1

For points \((-11, -5)\) and \((-2, -19)\), the slope is: \[ \text{slope} = \frac{-19 - (-5)}{-2 - (-11)} = \frac{-14}{9} = -\frac{14}{9} \]
03

Calculate Slope for Side 2

For points \((-2, -19)\) and \(12, -10)\), the slope is: \[ \text{slope} = \frac{-10 - (-19)}{12 - (-2)} = \frac{9}{14} \]
04

Calculate Slope for Side 3

For points \(12, -10)\) and \(3, 4)\), the slope is: \[ \text{slope} = \frac{4 - (-10)}{3 - 12} = \frac{14}{-9} = -\frac{14}{9} \]
05

Calculate Slope for Side 4

For points \(3, 4)\) and \((-11, -5)\), the slope is: \[ \text{slope} = \frac{-5 - 4}{-11 - 3} = \frac{-9}{-14} = \frac{9}{14} \]
06

Compare Slopes for Opposite Sides

Compare the slopes of the opposite sides. Sides \((-11, -5)\) to \((-2, -19)\) and \(12, -10)\) to \(3, 4)\) both have a slope of \(-\frac{14}{9}\). Similarly, sides \((-2, -19)\) to \(12, -10)\) and \(3, 4)\) to \((-11, -5)\) both have a slope of \(\frac{9}{14}\). This means they are parallel.
07

Determine if It Is a Parallelogram

Since opposite sides are parallel, the figure is a parallelogram.
08

Check Perpendicularity of Adjacent Sides

To check if the parallelogram is a rectangle, multiply the slopes of two adjacent sides. If the product is \(-1\), the sides are perpendicular. Calculate \(-\frac{14}{9} \times \frac{9}{14} = -1\).
09

Conclusion

Since the product of the slopes of adjacent sides is \(-1\), the adjacent sides are perpendicular, indicating the figure is a rectangle.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Slope Formula
The slope of a line represents its steepness and direction. The formula to calculate the slope between two points on a plane, \((x_1, y_1)\) and \((x_2, y_2)\), is given by:
\[ \text{slope} = \frac{y_2 - y_1}{x_2 - x_1} \]
This formula helps compare the inclines of different lines:
  • If two lines are parallel, their slopes are equal.
  • If two lines are perpendicular, the product of their slopes is \(-1\).
In the exercise, you calculated the slopes of the sides of a given quadrilateral and identified it as a parallelogram by comparing the slopes of opposite sides. By confirming the condition for perpendicular lines, you also concluded that the figure is a rectangle.
Parallelogram
A parallelogram is a four-sided figure where opposite sides are parallel. This means:
  • The slopes of opposite sides are equal.
  • Opposite angles are equal.
  • The diagonals bisect each other.
To determine if a figure is a parallelogram using coordinate geometry, you can calculate the slopes of all four sides. If each pair of opposite sides has equal slopes, the figure is a parallelogram. In this exercise, by using the slope formula, you found that the opposite sides have equal slopes, \(-\frac{14}{9}\) and \(\frac{9}{14}\), which confirmed the figure is a parallelogram.
Rectangle Geometry
A rectangle is a type of parallelogram with right angles at all four corners. This fact gives it these unique properties:
  • All angles are 90 degrees.
  • Opposite sides are equal and parallel.
  • The diagonals are equal in length and bisect each other.
To verify if a parallelogram is a rectangle in coordinate geometry, check if adjacent sides are perpendicular. You do this by multiplying their slopes. If the result is \-1\, the sides are perpendicular. In the problem, you multiplied the slopes of adjacent sides, \(-\frac{14}{9}\) \times \(\frac{9}{14}\), and the product was \-1\. Thus, the figure is confirmed as a rectangle.
Coordinate Geometry
Coordinate geometry combines algebra and geometry using a coordinate system to solve geometric problems. Important concepts include:
  • Using coordinates \((x, y)\) to denote points on a plane.
  • Finding the distance between points with the distance formula, \[ d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2} \]
  • Calculating the midpoint of a segment with \[ \text{midpoint} = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right) \]
  • Determining slopes and analyzing the orientation of lines.
In the given problem, you used coordinate geometry techniques: calculating slopes to establish the nature of a figure, confirming it as a parallelogram and validating it as a rectangle by checking the perpendicularity of sides.

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