Shortcut Trick
In a kite, if a diagonal splits unequal adjacent angles (∠ABD ≠ ∠ADB), it must be the axis of symmetry.
This means the diagonal BD divides the kite into two identical triangles, making ∠C = ∠A.
In ΔABD, the sum of all angles is 180°.
⇒ ∠A = 180° − (54° + 50°) = 76°
⇒ ∠C = 76°
∴ The correct answer is 76°.
Alternate Method
Given:
ABCD is a kite.
∠ABD = 54°
∠ADB = 50°
Method Used:
A kite has two pairs of equal adjacent sides, and its main diagonal divides it into two congruent triangles.
The sum of all interior angles in any triangle is always 180°.
Calculation:
⇒ For the given kite ABCD, if AB were equal to AD, ΔABD would be an isosceles triangle, making ∠ABD = ∠ADB.
⇒ However, given ∠ABD (54°) ≠ ∠ADB (50°), we conclude that AB ≠ AD.
⇒ Therefore, the adjacent equal sides must be AB = BC and AD = CD.
⇒ In this configuration, the diagonal BD acts as the axis of symmetry.
⇒ Because BD is the axis of symmetry, it divides the kite into two congruent triangles: ΔABD ≅ ΔCBD.
⇒ In ΔABD, the sum of internal angles is 180°.
⇒ ∠DAB + ∠ABD + ∠ADB = 180°
⇒ ∠DAB + 54° + 50° = 180°
⇒ ∠DAB + 104° = 180°
⇒ ∠DAB = 180° − 104° = 76°
⇒ Due to the exact congruence of ΔABD and ΔCBD, the corresponding angles are perfectly equal, meaning ∠DCB = ∠DAB.
⇒ ∠DCB = 76°
∴ The correct answer is 76°.
Additional Information
Properties of a Kite
A kite is a quadrilateral with two distinct pairs of equal-length sides that are adjacent to each other. The opposite angles where the unequal sides meet are always equal.
Diagonals of a Kite
The diagonals of a kite are always perpendicular to each other, intersecting at exactly 90°. The main diagonal (axis of symmetry) acts as the perpendicular bisector of the other diagonal.
Axis of Symmetry
The diagonal connecting the common vertices of the equal sides acts as the axis of symmetry. It bisects the angles at its endpoints and cleanly divides the kite into two identical congruent triangles.