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Question

The adjacent angles of a rhombus are in the ratio of 3 : 6. The smallest angle of the rhombus is:

The correct answer is

60°

Solving Rhombus Angles using Ratio

The question asks us to find the smallest angle of a rhombus where the adjacent angles are in the ratio 3:6.

A key property of a rhombus is that its adjacent angles are supplementary. This means that the sum of any two adjacent angles in a rhombus is always \(180^\circ\).

Let the two adjacent angles of the rhombus be represented by \(3x\) and \(6x\), based on the given ratio of 3:6.

Since the adjacent angles are supplementary, we can write the equation:

\(3x + 6x = 180^\circ\)

Now, we solve for \(x\):

  • Combine like terms: \(9x = 180^\circ\)
  • Divide both sides by 9: \(x = \frac{180^\circ}{9}\)
  • Calculate the value of x: \(x = 20^\circ\)

Now that we have the value of \(x\), we can find the measure of each adjacent angle:

  • First angle: \(3x = 3 \times 20^\circ = 60^\circ\)
  • Second angle: \(6x = 6 \times 20^\circ = 120^\circ\)

So, the two adjacent angles of the rhombus are \(60^\circ\) and \(120^\circ\).

The angles of the rhombus are alternating between these two values because opposite angles in a rhombus are equal. Therefore, the four angles of the rhombus are \(60^\circ, 120^\circ, 60^\circ, 120^\circ\).

We are asked to find the smallest angle of the rhombus. Comparing the two angle measures we found, \(60^\circ\) and \(120^\circ\), the smallest angle is \(60^\circ\).

Let's verify that these angles are indeed adjacent and supplementary:

  • Adjacent angles: \(60^\circ\) and \(120^\circ\). Their sum is \(60^\circ + 120^\circ = 180^\circ\). This confirms they are supplementary.
  • The ratio of adjacent angles: \(60^\circ : 120^\circ\) simplifies to \(1 : 2\). Wait, the ratio given is 3:6, which also simplifies to 1:2. So the calculation is consistent with the simplified ratio. If we use 3x and 6x directly: \(3x : 6x\) is indeed \(3:6\). Our angles \(60^\circ\) and \(120^\circ\) are in the ratio \(60:120\), which simplifies to \(6:12\), and further to \(1:2\). The ratio 3:6 also simplifies to 1:2. So the ratio is correctly represented.

The smallest angle is \(60^\circ\).

Adjacent Angles of Rhombus Calculation
Property Used Given Ratio Setup Solution for x Adjacent Angles Smallest Angle
Adjacent angles are supplementary (\(180^\circ\)) 3 : 6 \(3x + 6x = 180^\circ\) \(9x = 180^\circ \implies x = 20^\circ\) \(3x = 60^\circ\)
\(6x = 120^\circ\)
\(60^\circ\)

Revision Table: Rhombus Properties

Key Properties of a Rhombus
Property Description
Sides All four sides are equal in length.
Opposite Angles Opposite angles are equal in measure.
Adjacent Angles Adjacent angles are supplementary (sum to \(180^\circ\)).
Diagonals Diagonals bisect each other at right angles (\(90^\circ\)).
Diagonals and Angles Diagonals bisect the angles through which they pass.

Additional Information: Understanding Rhombus Angles

A rhombus is a special type of parallelogram. This means it inherits all the properties of a parallelogram, such as opposite sides being parallel and equal, and diagonals bisecting each other. However, a rhombus has additional unique properties, primarily concerning its sides and angles.

In any quadrilateral, the sum of all interior angles is \(360^\circ\). For a rhombus with angles \(A, B, C, D\), if angles A and B are adjacent, then \(A + B = 180^\circ\). Since opposite angles are equal, \(A=C\) and \(B=D\). So the angles are \(A, B, A, B\). The sum is \(A+B+A+B = 2(A+B)\). Since \(A+B=180^\circ\), the sum is \(2 \times 180^\circ = 360^\circ\), which holds true for all quadrilaterals.

In our case, the angles are \(60^\circ, 120^\circ, 60^\circ, 120^\circ\). The sum is \(60 + 120 + 60 + 120 = 360^\circ\).

Understanding the supplementary nature of adjacent angles is crucial for solving problems involving rhombus angles and ratios.

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Important Questions from Quadrilaterals

  1. The area of a rectangle is 300 cm 2and the length of its diagonal is 25 cm. The perimeter of the rectangle (in cm) is:

  2. The area of a trapezium is 18 sq.cm. Its height and base are 3 cm and 5 cm respectively. Find the length of the side parallel to the base.

  3. Find the area of a rhombus whose perimeter is 116 cm and one diagonal is 42 cm in length.

  4. The ratio of sides to a quadrilateral is 2 4  5 and the perimeter is 560 cm. Find out the smallest side. (In cm) 

  5. The ratio of arms of a quadrilateral is 2 5 and the Perimeter is 616 cm. Find out the smallest arm. (In cm)

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