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Question

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?

The correct answer is 280 cm 2

Calculating the Area of the Rectangle

The problem involves a rhombus and a rectangle. We are given information about the rhombus and need to use it to find the dimensions and area of the rectangle.

Step 1: Find the Lengths of the Diagonals of the Rhombus

A rhombus has four equal sides, and its diagonals bisect each other at right angles. This property creates four congruent right-angled triangles inside the rhombus. The hypotenuse of each triangle is the side of the rhombus, and the legs are half the lengths of the diagonals.

  • Side of the rhombus = 26 cm.
  • Length of one diagonal (\(d_1\)) = 20 cm.
  • Half of this diagonal = \(\frac{20}{2} = 10\) cm.

Let the other diagonal be \(d_2\). Half of this diagonal is \(\frac{d_2}{2}\) cm.

Using the Pythagorean theorem in one of the right-angled triangles:

$\$(\text{Side})^2 = (\frac{d_1}{2})^2 + (\frac{d_2}{2})^2\$\$$

Substituting the given values:

$\$26^2 = 10^2 + (\frac{d_2}{2})^2\$\$$

$\$676 = 100 + (\frac{d_2}{2})^2\$\$$

$\$(\frac{d_2}{2})^2 = 676 - 100\$\$$

$\$(\frac{d_2}{2})^2 = 576\$\$$

Taking the square root of both sides:

$\$ \frac{d_2}{2} = \sqrt{576} = 24 \text{ cm} \$\$$

So, the length of the other diagonal is:

$\$d_2 = 2 \times 24 = 48 \text{ cm}\$\$$

The lengths of the diagonals of the rhombus are 20 cm and 48 cm.

Step 2: Find the Sum of the Lengths of the Diagonals

The sum of the lengths of the diagonals is \(d_1 + d_2\).

$$ \text{Sum} = 20 \text{ cm} + 48 \text{ cm} = 68 \text{ cm} $$

Step 3: Relate Rhombus Diagonals to Rectangle Perimeter

The problem states that the sum of the lengths of the diagonals of the rhombus is equal to the perimeter of a rectangle.

Perimeter of rectangle = Sum of rhombus diagonals = 68 cm.

Let the length of the rectangle be \(l\) and the breadth be \(b\). The perimeter of a rectangle is given by the formula \(2(l + b)\).

$$ 2(l + b) = 68 \text{ cm} $$

Dividing both sides by 2:

$$ l + b = 34 \text{ cm} \quad \text{(Equation 1)} $$

Step 4: Use the Difference in Rectangle Dimensions

We are also given that the difference between the length and breadth of the rectangle is 6 cm.

$$ l - b = 6 \text{ cm} \quad \text{(Equation 2)} $$

Step 5: Solve for the Length and Breadth of the Rectangle

We have a system of two linear equations:

Equation 1: \(l + b = 34\)

Equation 2: \(l - b = 6\)

Adding Equation 1 and Equation 2:

$$ (l + b) + (l - b) = 34 + 6 $$

$$ 2l = 40 $$

$$ l = \frac{40}{2} = 20 \text{ cm} $$

Substitute the value of \(l\) into Equation 1:

$$ 20 + b = 34 $$

$$ b = 34 - 20 = 14 \text{ cm} $$

So, the length of the rectangle is 20 cm and the breadth is 14 cm.

Step 6: Calculate the Area of the Rectangle

The area of a rectangle is calculated by multiplying its length and breadth.

$$ \text{Area} = l \times b $$

$$ \text{Area} = 20 \text{ cm} \times 14 \text{ cm} $$

$$ \text{Area} = 280 \text{ cm}^2 $$

The area of the rectangle is 280 cm\(^2\).

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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. A quadrilateral whose four sides and angles are equal to each other is known as

  3. The sides of a quadrilateral are in the ratio of 3 ∶ 4 ∶ 6 ∶ 8. If the perimeter of the quadrilateral is 84 cm. Find the longest side of the quadrilateral.

  4. 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:

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

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