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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 ratio between the length and breadth of a rectangular park is 3 : 2. If a man cycling along the boundary at the speed of 12 km per hour completes one round in 8 minutes, then the area of the park in square meter will be

  2. The side of a rhombus is 26 cm. The length of one of its diagonals is 20 cm. The sum of the lengths of the diagonals of this rhombus is equal to the perimeter of a rectangle. If the difference between the length and breadth of the rectangle is 6 cm, then what is the area of the rectangle?

  3. PQRS is a cyclic quadrilateral. If ∠P is 4 times ∠R, and ∠S is 3 times ∠Q, then the average of ∠Q and ∠R is:

  4. ABCD is a trapezium in which AB || DC and DC is perpendicular to BC. If ∠DAB = 110°, then ∠ABC - ∠ADC =_____.

  5. If the quadrilateral has an inscribed circle, then the sum of a pair of opposite sides equals:

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