Chapter 1: Problem 11
Recall that a rhombus is a planar quadrilateral whose sides all have the same length. Use the dot product to show that the diagonals of a rhombus are perpendicular to each other.
Short Answer
Expert verified
The diagonals of a rhombus are perpendicular because their dot product equals zero.
Step by step solution
01
Define the Rhombus Vertices
Consider a rhombus with vertices \( A(0,0) \), \( B(a,0) \), \( C(a+b_h,b_v) \), and \( D(b_h,b_v) \). This setup uses vectors to define each point, ensuring all sides have equal length.
02
Verify Equal Side Lengths
Compute the distances for each side using the distance formula: \( AB \), \( BC \), \( CD \), and \( DA \). Ensure each distance is \( a \) to confirm it is a rhombus.
03
Determine Vector Representations
Write the vectors for the diagonals: \( AC = (a+b_h, b_v) \) and \( BD = (b_h-a, b_v) \). These represent the rhombus's diagonals.
04
Calculate the Dot Product of Diagonals
Find the dot product of vectors \( AC \) and \( BD \):\[(a + b_h, b_v) \cdot (b_h - a, b_v) = (a + b_h) \cdot (b_h - a) + b_v^2 = a b_h - a^2 + b_h b_h - b_h a + b_v^2\]Simplify to find if the dot product equals zero.
05
Show Perpendicularity
For the diagonals to be perpendicular, the dot product must be zero. Simplify:\[-a^2 + b_h^2 + b_v^2 = 0 \]Since this equation equals zero, the diagonals of the rhombus are perpendicular.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Dot Product
The dot product is a way to multiply two vectors together, resulting in a scalar value. It's used to determine the angle or relationship between two vectors. If the dot product is zero, the vectors are perpendicular. For two vectors \((\mathbf{u})\) and \((\mathbf{v})\), the dot product is calculated as:\[\mathbf{u} \cdot \mathbf{v} = u_1v_1 + u_2v_2 + \ldots + u_nv_n\]
- Each term pairs corresponding components from the vectors.
- The result is a single number.
Quadrilateral
A quadrilateral is any four-sided shape in a plane. In geometry, quadrilaterals can take many forms, such as squares, rectangles, parallelograms, and rhombuses. Each quadrilateral has:
- Four vertices
- Four sides
- Two diagonals
Diagonals Perpendicular
Diagonals intersecting at right angles (perpendicular diagonals) create significant geometric properties. In a rhombus, this characteristic arises naturally due to the figure's symmetry.When the diagonals of a quadrilateral are perpendicular, it implies that their intersecting angle is \(90^\circ\). This can be verified using the dot product, as explored in the solution to our exercise:
- Calculate the dot product of the diagonals.
- If the dot product equals zero, the diagonals are indeed perpendicular.
Equal Side Lengths
Equal side lengths mean that each side of a shape has the same measure. For a quadrilateral like a rhombus, this is a defining property. All four sides being the same length ensures certain symmetry and geometrical properties.To confirm equal lengths, the distance between vertices can be calculated using the distance formula:\[d = \sqrt{(x_2-x_1)^2 + (y_2-y_1)^2}\]
- Apply this formula for each side of the quadrilateral.
- Verify that all calculated distances are equal.