finding area when diagonals are given, calculating perimeter from given conditions, property-based questions, and coordinate geometry problems involving quadrilaterals
⚡Powerful Shortcut - Diagonal Rule
For any quadrilateral with perpendicular diagonals, Area = (1/2) × d1 × d2. This works for rhombus, kite, and square. This single formula can solve multiple question types quickly.
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Worked Example
Solve this step-by-step before moving on
1
Step 1
Find Area
Area = (1/2) × d1 × d2
Area = (1/2) × 16 × 12 = 96 cm²
2
Step 2
Find Side Length
Diagonals of rhombus bisect at right angles.
Half diagonals: 8 cm and 6 cm
Using Pythagoras: Side = √(8² + 6²) = √(64 + 36) = √100 = 10 cm
3
Step 3
Find Perimeter
Perimeter = 4 × side = 4 × 10 = 40 cm
Another Time-Saving Trick:
When a quadrilateral's vertices are given in coordinate geometry, use the shoelace formula: Area = (1/2)|x1(y2-y4) + x2(y3-y1) + x3(y4-y2) + x4(y1-y3)|. This eliminates the need for multiple calculations.
Common Mistake:
Students often confuse rhombus and square properties. Remember: Square has all properties of rhombus PLUS all angles are 90°. Rhombus doesn't necessarily have 90° angles. Also, many forget that in trapezium area formula, height is the perpendicular distance between parallel sides, not the slant side length.
A rectangle has length 24 cm and breadth 16 cm. What is the perimeter of the rectangle?
Practice 2easy
A square has a side length of 15 m. What is its area?
Practice 3easy
A trapezium has parallel sides of 14 cm and 10 cm, and a height of 8 cm. What is its area?
Practice 4easy
A rhombus has diagonals of length 18 cm and 24 cm. What is its area?
Practice 5easy
A rectangle has length 28 m and breadth 12 m. If a square of side 5 m is cut out from one corner, what is the remaining area?
Practice 6easy
A parallelogram has a base of 20 cm and a height of 12 cm. What is its area?
Practice 7medium
A kite ABCD has diagonals AC and BD intersecting at O. The diagonals are 24 cm and 18 cm respectively. If the diagonals divide the kite such that AO = 16 cm and BO = 12 cm, find the area of the kite.
Practice 8medium
A parallelogram has adjacent sides of 12 cm and 8 cm. If the angle between them is 60°, find the area of the parallelogram.
Practice 9hard
A rectangle PQRS has length 24 cm and width 10 cm. A point X lies on side QR such that QX = 6 cm. Find the length of diagonal PX (in cm).
Practice 10hard
In a kite ABCD, the diagonals AC and BD intersect at O. Given that AC = 20 cm, BD = 16 cm, and the diagonals intersect such that AO = 12 cm and BO = 6 cm, find the area of the kite (in cm²).
Practice 11hard
A trapezium ABCD has parallel sides AB = 24 cm and CD = 16 cm. The perpendicular distance between them is 10 cm. A line parallel to both AB and CD divides the trapezium into two parts of equal area. Find the length of this dividing line (in cm).
60-Second Revision — Quadrilaterals
Remember: All quadrilateral interior angles sum to 360°
Formula: Area with perpendicular diagonals = (1/2) × d1 × d2
Trap: Square is both rectangle and rhombus, but rhombus is not always rectangle
Quick check: Parallelogram opposite sides are parallel AND equal
Memory aid: Rectangle = right angles, Rhombus = equal sides